Jon Lester had been little short of masterful through four no-hit innings on Tuesday night, and so when he did not emerge from the dugout for the fifth inning, and was instead replaced by Matt Albers, confusion followed by concern spread quickly across New England.

For three years, the left-hander has been the tireless anchor of the pitching staff. He made at least 32 starts from 2008-10, managing to avoid the disabled list in all three seasons. This year was no different. On a Red Sox staff that had seen three of its five Opening Day members (John Lackey, Clay Buchholz, Daisuke Matsuzaka) land on the DL, and another (Josh Beckett) miss a couple of starts due to illness, Lester had been the constant.

And so, the news that the left-hander had endured a strained left latissimus dorsi muscle immediately gave a sense that a starting rotation that was supposed to be a Red Sox strength this year had instead become an uncertainty. There are only so many injuries, seemingly, that a rotation can withstand at one time. With Matsuzaka out for the year after undergoing Tommy John and Buchholz out indefinitely (pending his exam in Charlotte on Wednesday) due to a sore lower back, the Sox seemed near the breaking point.

The initial postgame reaction from Lester, then, following his team’s nail-biting 3-2 victory over the Blue Jays (recap), seemed to offer the Sox some grounds for reassurance. Though acknowledging the he is sore, the 27-year-old insisted that, aside from his last scheduled start prior to the All-Star break, he anticipates no real impediment to his availability.

"We’ll get it looked at tomorrow, see how I feel. Luckily, we have the All-Star break built in, so hopefully we don’t have to do anything drastic around here," Lester said. "We may alter one start, but like I said, we’ve got the All-Star break built in. … I don’t imagine this being a long-term deal. We’ll re-evaluate everything tomorrow. Hopefully, this was just a more precautionary type deal, just a fluke thing, and move on."

The Sox will gain greater clarity on Wednesday, when Lester undergoes more extensive tests to determine the extent of his injury. Clearly, the prognosis will have significant implications for how the Sox proceed this season.

If Lester (10-4, 3.31) is sidelined for no more than a start or two, then the impact will be negligible. After all, the Sox typically try to build extra rest into the All-Star break for the left-hander in deference to his significant workload.

If he is out longer, then the Sox will face a host of different questions that could more significantly alter the team’s landscape. Just hours before Lester’s outing, general manager Theo Epstein, in an appearance on NESN, said that the Sox expected that they were more likely to seek a bat at the trade deadline than an arm.

“I think for us, probably position players [are the most likely trade targets] at this point. I don’t see a ton of pitching help out there,” Epstein told NESN. “The few guys who can really make an impact, it would take half your farm system or your whole farm system. ... I don’t see it as realistic. I think we would benefit from a complementary position player who would really fill a need for us in the right spot.

“We could end up with a pitcher. We could end up with a position player. But just looking at the landscape, there are probably more position players that could fit for us than pitching right now. There is some pitching depth [in the organization]. There are some areas, because of injuries, both up here and in the minor leagues, we don’t have as much position playing depth at the moment. Now, two, three weeks from now, if we get healthy, we might have that depth here.”

That was before Lester’s injury. How, if at all, might the left-hander’s lat strain affect that outlook?

Here are five thoughts on the matter:

THE MOST LIKELY SOLUTIONS ARE INTERNAL

The fact that Lester is sidelined is unlikely to prompt Sox officials to make panic-stricken calls to other GMs seeking arms, for a couple of reasons.

First, a team source indicated on Wednesday that the team has limited financial room to maneuver at the trade deadline. Even with Lester out, the Sox have spent so heavily on the 2011 roster that the team’s approach to the July 31 trade deadline is likely to be restricted to upgrades at the margins.

Second, the available options are few. As Epstein suggested, a market for impactful starters simply has yet to materialize.

Third, and perhaps most significantly for the organization, the Sox have a number of capable pitchers in the majors and Triple-A who are capable of filling in and offering the Sox reasonable alternatives. Alfredo Aceves (3-1, 3.74), despite a 5.14 ERA in four starts, has kept the Sox in the game in three of his four starts. He represents a legitimate in-house alternative who is already on the big league roster.

Then, in Triple-A, the Sox have three pitchers who are emerging as options. On the 40-man roster, the team has left-hander Felix Doubront. The 23-year-old left-hander is 0-3 with a 3.86 ERA, 45 strikeouts and 18 walks in 48 innings. He’s been limited to 11 starts due to some early-season injuries.

Doubront had been pitching very well for most of the year, though he appears to have hit something of a wall of late. He has given up six homers in his last four starts, and after carrying a 2.68 ERA into late June, he has given up 10 runs in his past 12 innings.

Still, the Sox feel strongly that he has the three-pitch mix (fastball, curve, changeup) of a starter. Assuming that he is merely enduring a normal mid-summer hiccup, he represents a pitcher whom the Sox would feel comfortable adding to the big league mix.

The team also has two options who are not on the 40-man roster. Right-hander Kyle Weiland has been consistently excellent for the PawSox this year, going 8-6 with a 3.00 ERA, striking out 99 and walking 37 in 93 innings. He has held opponents to a .206 batting average.

Weiland has been strikingly consistent. His improved ability to get left-handers out this year (.175 batting average against) thanks to three factors — the introduction of a cutter, improved glove-side fastball execution and an ability to backdoor his big breaking ball consistently — has convinced multiple team sources that he has a future as a back-end-of-the-rotation starter, capable of delivering 180-200 quality innings on an annual basis.

Weiland’s name has come up as a potential call-up several times this year. If Lester is unavailable for any prolonged stretch, he undoubtedly would once again be in the mix for a potential big league debut.

Veteran Kevin Millwood, meanwhile, is 4-0 with a 4.15 ERA, 36 strikeouts and 12 walks in 39 innings. He has allowed three or fewer runs in five of his seven outings. His performance suggests that he could benefit the Sox in a role along the lines of what Paul Byrd contributed to the Sox in 2008 and 2009, when the veteran served as duct tape for a thinning rotation down the stretch. 

“I think right now, that’s a strength of the organization — the starting depth that we have,” Epstein said on NESN. “I think there are options if we have to fill in. It’s already proven to be an aid to our effort so far.”

THE HEALTH OF CLAY BUCHHOLZ ALSO LOOMS LARGE

The lower back injury that initially seemed trivial — Buchholz, after all, had been pitching through the condition, and pitching very well — has persisted. It has shown little improvement. The longer that Buchholz — an All-Star a year ago who finished second in the AL in ERA — has remained sidelined, the more anxious the situation has become for team decision-makers.

The Sox believe that the issue is a muscular one, rather than a potentially more significant structural issue such as a disc. Greater clarity is expected on Wednesday, when Buchholz consults a specialist in North Carolina. In a best-case scenario for the Sox, Buchholz will get a relatively clean bill of health that will also provide sufficient reassurance to permit him to return to the rotation shortly after the All-Star break.

“I don’t know there’s many players that play right now that don’t have some soreness somewhere,” Sox manager Terry Francona said prior to Tuesday’s game. “But we want to make sure if he pitches — because he’s probably going to be sore for a while — that he’s not hurting himself. Not only for his sake but for ours. Want to make sure we’re not missing something, or somebody has a different opinion. That’s why you do these things. You try to get intelligent people and get the best opinions you can.”

It has now been almost three weeks since Buchholz last pitched. If his return gains greater definition, then the Sox will no doubt feel a bit more at ease about their ability to manage Lester’s situation.

ANDREW MILLER AND TIM WAKEFIELD HAVE BEEN, AND WILL CONTINUE TO BE, VERY IMPORTANT PITCHERS FOR THE SOX

Wakefield, who takes the mound on Wednesday, now has made 10 starts, going 4-3 with a 4.84 ERA. The Sox are 6-4 when he takes the mound, an accurate reflection of his ability to keep the team in the game in most of his outings.

Andrew Miller is 2-0 with a 3.06 ERA for the Sox, who have won all three of his starts. The left-hander has impressed with both his stuff and his poise.

“It’s awesome. There’s basically no drop-off from me to him,” Buchholz said of Miller’s performance. “He’s a guy who can go out and dominate with the pitches he has. All of them pretty much are major league plus pitches.

“I think the organization feels the same way — he’s a guy who can step in, fill a spot that I’ve had to work up to in my career, where the organization felt like it had a chance every time I rolled out there. I think the organization feels the same way about him.”

Already — given Matsuzaka’s absence for the season, the uncertainty surrounding Buchholz’ return and the ongoing struggles of John Lackey — Wakefield and Miller were emerging as significant contributors. Lester’s injury only amplifies that perception. If the Sox are to withstand what appears to be a challenging stretch of summer attrition, at least one of those two pitchers will have to continue to serve as a stabilizing influence on the rotation. 

JOHN LACKEY ISN’T GOING ANYWHERE … FOR NOW

Though he has struggled en route to the worst ERA (7.47) of any major league starter, the Sox had no plans to pull the plug on John Lackey in the rotation. Lester gives the Sox even less freedom to re-examine its rotation options.

That said, Epstein (in his NESN appearance) also suggested that the Sox can’t simply resign themselves to keeping the right-hander in the rotation forever if he continues to struggle to this extent.

“As an organization we’ve got to find some answers. A lot of times this year, he just hasn’t been good enough and has taken us out of games,” Epstein said. “Right now, there aren’t answers. Otherwise he would have applied some things and taken some steps forward. There are questions, not answers. It’s our job to find the answers.

“We’ve got to keep working at it and get better. It’s definitely got to get better. He has a chance to be an important part of this team, wants to be, and has the talent to. It’s just not happening right now,” Epstein added. “If he’s able to go out there and keep us in games, then yeah, he should get the ball. If he’s not, then we’ve got to look deeper. But he’s in the rotation. He’s got a chance to go out there and make it better.”

THE SOX WILL WAIT WITH BATED BREATH

The fact that Lester was so adamant that he will not be sidelined for any significant length was no doubt reassuring for the Sox. Even so, that reassurance can only go so far. The reality is that, much as has been the case with Buchholz’ injury, the Sox won’t have any guarantees about when Lester is going to return until he is actually next seen on a mound.

Lat strains can be relatively trivial. As reliever Matt Albers (who went on the 15-day DL in April with just such an injury) noted, it is possible to address them in as little as a few days.

“For me it wasn’t really that long before I felt 100 percent again,” Albers said. “I told Jon that, that maybe it was five or six days before I played catch and didn’t feel anything again. Hopefully that’s it and it’s just one [missed] start [for Lester].”

On the other hand, lat strains also have been known to cost pitchers months at a time. Until the Sox give Lester a more comprehensive exam on Wednesday and then see how he responds to rest and treatment, they simply cannot be sure how long he’ll be sidelined.

Lester was relieved that he was pulled when he was, noting that had he returned to the mound for the fifth inning, he might have been in danger of a more significant injury. Certainly, that is the Sox’ hope as well.

If he is out for only a brief period of time, missing perhaps one or a couple of starts, then the Sox will sigh that they dodged a bullet, and note that there might be a long-term benefit to the fact that Lester’s prized left arm enjoyed a midyear respite. If, however, his injury keeps him out for longer, then the team’s outlook could change considerably.

For while the team has potential internal solutions should Lester be absent from the rotation for any extended duration, the Sox do not have another pitcher like Lester. He ranks among the game’s elite for a reason. While alternatives can be identified, none would come with the top-of-the-rotation stature of the Sox’ Opening Day starter.