Derrick Burgess and Logan Mankins have now been missing from almost the first full week of Patriots’ training camp. While there remains the possibility the two could return, the Patriots have already started to pursue some alternate plans at outside linebacker/defensive end and offensive line in case Burgess does decide to retire or Mankins chooses to sit out for an extended stretch.

On Sunday, they worked out defensive end Adewale Ogunleye, and on Tuesday, they reportedly did the same for a trio of young offensive linemen. According to director of player personnel Nick Caserio, when it comes to adding players at this time of year, it’s all about keeping your options open.

“Really, you’re open for business on anything,” Caserio said when asked about team-building possibilities during training camp and into the preseason. “There are a number of different avenues that continue to build your club, whether that’s through trades, whether it’s free agency, whether it’s waiver wire claims. So I think its just normal procedure to go through this time of year. Whether that entails trade talks … I wouldn’t say this year is different than any other year.”

At this point on the calendar, if it wants to add bodies to replace Burgess or Mankins, New England is likely faced with three courses of action: make a trade, look for available free agents or scour the waiver wire. When it comes to making deals, the Patriots have made a couple of notable summertime trades — in 2003, they were able to acquire Ted Washington on August 20 for a fourth-round pick in the 2004 draft, and the massive nose tackle would go on to have a great season in New England. And last year, they also picked up Burgess for a pair of draft picks in an August trade.

While there is still time to make a trade, at this stage of camp, the Patriots appear to be more focused on available free agents. The last few seasons, they have been able to find good value with players picked up after the start of camp, a group that includes outside linebacker Rob Ninkovich.

“If you look at last year during training camp — I think it was August 2 or whatever it was — we brought Rob Ninkovich in, worked him out, and he ended up making the roster,” Caserio said, “and he’s been here since and has carved out a little niche and a role for himself.”

To that end, the Patriots reportedly kicked the tires on three offensive linemen on Tuesday, bringing in center Eric Ghiaciuc and guard Darnell Stapleton (both free agents) along with offensive tackle Mark Ortmann (an undrafted free agent) for workouts, according to Adam Caplan of Foxsports.com. Considering the instability of the line through the early stages of camp (Logan Mankins’ absence, the injury to Nick Kaczur) it wouldn’t be surprising if New England decided to go after another o-lineman with the idea of building as much depth as possible.

There are also possibilities on the other side of the ball. League sources indicate that while the Patriots worked out Ogunleye (a veteran free agent) on Sunday morning, they are not currently pursuing some of the bigger name free agent pass rushers who are still on the market, namely Greg Ellis and Chike Okeafor.

One name that has come up more and more is defensive end Aaron Schobel, who is apparently set to part ways with the Bills. It seems like a bit of a stretch at this point —Buffalo would move heaven and earth to prevent him from signing with a division rival.

And while two football statisticians believe that while Schobel had a good year in 2009, he may not be the right fit for the New England 3-4 defense.

“He had a fine season last year — we have him credited with 30 Defeats, which are stops for no gain, a loss, or short of a first down on third down, which is a high number for a defensive end. His average tackle came 0.2 yards downfield, which was best in the NFL,” Mike Tanier of Football Outsiders said of Schobel. “He’s really not a 3-4 player, though. He’s not quick enough for outside linebacker, and would get hammered playing as a five-technique end for play after play.”

“He’s was still a better than average player last year, but looks to be on a decline; how far that continues is anyone’s guess,” wrote Neil Hornsby of Pro Football Focus in an e-mail. “Was the dip due to the 2008 injury or is it age? Will he come back even stronger in 2010 or is that better than average performance going to become a worse than average to poor type showing at a high-dollar value? I think with Buffalo moving to 3-4, the OLB position combined with the above is too big a risk. If they just want him to play with his hand down in passing situations that’s a bit of a waste as his real skill comes from being a good run defender and every down player.

“The call of Schobel to NE would depend very much for me on what defense the Patriots want to play. If it’s predominantly 3-4 then I’m not sure it’s any less of a risk than in Buffalo,” adds Hornsby. “To me, the best fit for Schobel would be the Ravens. They play the 4-3 much (much) more than anyone thinks and as fine a player as Jarret Johnson, is rushing the passer isn’t his best part of his game. In addition, there’s Chicago (is Mark Anderson going to stand up as an every-down DE?), Seattle (their DL looks like a disaster zone) or St. Louis (Let Chris Long play DLE instead of James Hall).

“Bottom line: I’d take him, but only in a straight 4-3 defense.”

The third way to augment your roster at this time of year is to keep an eye on who gets cut. While teams are allowed to release players at any time, there are two key dates to keep an eye out for this year — August 31, when rosters have to be cut down to 75 players, and September 4, when teams must be at 53 players.

In the end, it all contributes to this time of year being one of the most dynamic and fluid times of the year for an NFL front office.

“There is so much shuffling and movement that goes on at different points,” Caserio said. “You just have to look at your own situation and figure out what makes the most sense for the club. And that’s what we’ve done, that’s what we’ll always do, and that’s what we’ll continue to do. If there’s an opportunity for us that makes sense, we’ve done it before.

“It all depends on the situation.”