Before there was Junior Seau, there was Clay Matthews.

The 40-year-old Seau returned to the Patriots this week, giving new meaning to the term “veteran linebacker.” Previously, Seau has played portions of the last three seasons for New England. The last linebacker to play for Bill Belichick this late in his career was Matthews, who suited up for Belichick and the Browns in 1993 when he was 37.

While Seau has some time in the system, Matthews was able to shed some light Thursday on what Seau is facing as he prepares for his 20th season in the NFL.

“The challenge for Junior isn’t in the games. The games should be fine. The practices are tougher,” Matthews said of what awaits Seau. “It’s be getting through the practices week in and week out.

“The games are exciting. You’re in a fast, exciting environment. But really going out and practicing the way you need to practice, you tend to get a lot of aches and pains, and at that age, you don’t know if those are just aches and pains or something more.”

In an attempt to guard against those aches and pains, Seau — a well-known workout fiend — threw himself back into things with a vengeance when he returned to Foxboro this week, hitting the weight room at 5:30 on Wednesday morning and working up a good sweat before quarterback Tom Brady arrived at 6:45.

But he knows the only way to get into game shape is to strap on the helmet and get after it.

“In the game of football, you really cannot train to be in football shape unless you have a helmet on and you have 10 other guys shooting for your knees,” said Seau, who said he’s going to try and be ready to play on Sunday against Tennessee.

Matthews played 19 seasons in the NFL, 16 of with the Cleveland Browns (from 1978 to 1993) and three with the Atlanta Falcons (1994 to 1996). His last three seasons in Cleveland were spent playing for Belichick in his first head coaching job. The Patriots coach still waxes poetic about his time with Matthews, calling him one of the best linebackers he’s ever coached and saying he was “lucky” to have had the chance to coach Matthews.

One of the things that made Matthews as great as he was was the fact the he knew how to take care of his body. Even though Matthews doesn’t know Seau, he believes he’s the kind of player who has done a good job preparing his body for the rigors of the NFL.

“I never played with him,” Matthews said of Seau. “But I imagine the fact that he’s played this long means he can certainly take care of himself. He needs to do what he needs to do to take care of himself, day in and day out. I imagine he knows how to do that.”

As a head coach, Belichick has had several linebackers play for him well into their late 30s before retiring: in Cleveland, it was Matthews, Mike Johnson and Pepper Johnson. In New England, Tedy Bruschi, Roman Phifer and Seau have all had extended careers with Belichick.

The secret to succeeding late into their careers? Some of it is hard work. But Matthews believes some of it can also be attributed to winning the genetic lottery.

“I certainly think a lot of folks who play this long are blessed they have a body that holds up well,” said Matthews, currently a high school football coach in California. “Sure, we’ve done their part by staying in shape. But sometimes, I think that some of us were blessed to have bodies that could take a beating and keep going.”