Packers linebacker Clay Matthews. Photo by Corey Behnke of CheeseheadTV.com.

The contract is in the rearview mirror for Green Bay Packers linebacker Clay Matthews.

During the offseason, he received a five-year extension worth $66 million. There's no reason for distraction. Matthews is now the highest-paid linebacker in the NFL.

When training camp opens and the Packers practice for the first time on Friday July 26, Matthews can instead direct his attention on getting prepared for the season at hand––and staying healthy.

For four seasons, Matthews' hamstrings have been an ongoing issue.

During his rookie season, it took 19 days for the first round draft choice to recover from a pulled hamstring during training camp, which forced him to miss the first three preseason games, according to Tom Silverstein of the Milwaukee Journal Sentinel.

The same issue arose during training camp in 2010, that time taking 24 days to return to action, not playing in a single exhibition game. Matthews also missed one regular season game in 2010, a Week 6 matchup with the Miami Dolphins after aggravating the injury a week prior versus the Washington Redskins.

For a while, it appeared the issue may have abated. Later during the 2010 season, Matthews suffered from a shin injury that prevented him from fully participating in practice and later revealed to be a stress fracture. But at least the hamstring problems had subsided.

During the 2011 season, Matthews remained largely injury-free, which was a step in the right direction. Unfortunately for the four-time Pro Bowler, Matthews' clean bill of health only lasted until November of last season when he pulled his left hamstring and missed four games at midseason.

The silver lining for both Matthews and the Packers is that he's been able to play at a high level despite lingering concerns about his hamstrings, and the Packers have been able to stay afloat even when Matthews has been out of the lineup.

Whether Matthews' injury is evolving remains to be seen. In his first two seasons in the NFL, his hamstring pulls occurred in training camp, after a summer away from team facilities. Last year, however, the issue didn't crop up until November, maybe a sign of late-season fatigue.

There's little doubt that Matthews is an athletic demon. He has quick-twitch muscle movements that allow him to react faster than many of his opponents, along with a combination of size and speed superior to most other football players.

Perhaps a byproduct of Matthews' physicality is that he's too tightly wound, too muscle-bound for his own good, which makes him prone to pulls and strains. But then we come back to the fact that apart from 2012's four-game absence, Matthews has not missed any lengthy period of time during the regular season––when the games count.

Still, Matthews has missed time on four separate occasions due to hamstring pulls, which will no doubt put the Packers on alert and wary of anything that may trigger another setback.

Matthews had 13 sacks last season despite missing those four games, only half a sack off his single-season high of 13.5 set in 2010.

Entering his fifth season in the NFL, there's reason to believe Matthews is entering his prime. Combined with a star quarterback at the peak of his career, the window of opportunity available to the Packers in 2013 appears to be wide open.

It will be up to Matthews to combat the notion that athletes who receive large signing bonuses and the security of a long-term extension become complacent.

In the case of Matthews, such complacency could leave him vulnerable to injury. Yet there's no evidence that he will fall prey to the pitfalls of contentment.

Matthews will be counted upon to act as a leader at a position filled with inexperience. The Packers are seeking more production from the bookend linebacker, expected to 2012 first round draft choice Nick Perry, a fellow USC alum.

Beyond Perry, the outside linebackers include second-year player Dezman Moses, sixth round draft choice Nate Palmer, and undrafted rookies Andy Mulumba, Donte Savage and Jarvis Reed.

Gone this season are marginal performers Erik Walden and Frank Zombo, both of whom left as free agents. So is safety Charles Woodson who has been the heart and the soul of the Packers defense for the past several years.

That role will be left to Matthews. He'll have to lead a defense that will need to improve upon last year's ranking of 11th in overall defense, 17th in rushing defense and 26th in yards allowed per rush.

Such a task will be much easier if he's healthy.

Brian Carriveau is the author of the book "It's Just a Game: Big League Drama in Small Town America," and editor of Cheesehead TV's "Pro Football Draft Preview." To contact Brian, email [email protected].