Robert Mathis
Indianapolis Colts linebacker Robert Mathis smiles while sitting on the bench during the fourth quarter of their NFL preseason football game against the Cincinnati Bengals in Indianapolis, Indiana.Reuters

Indianapolis Colts outside linebacker Robert Mathis is expected to miss the rest of the NFL season due to tore Achilles tendon.

Mathis suffered a torn Achilles last week while working out away from team on his own in Atlanta, according to

The 33-year-old is currently suspended for violating the league's policy on performance-enhancing drugs. However, Mathis claims that it was fertility drugs he was taking to have a child which was the cause of the positive test result.

He has three games left on his suspension, after Colts' loss to the Denver Broncos on the opening weekend of the NFL season. 

Since the injury was caused while away from the team facility, the club can place Mathis on the non-football injury list and not pay him for the year.

Mathis recorded 19.5 sacks in 2013. The Colts gave him a four-year, $36 million deal prior to the 2012 season and he was due to make $5 million this year and $7 million in 2015.

Meanwhile, Mathis is also not allowed to enter the locker room during his suspension but he left a note on his locker to pass a message to his teammates.

"Athletes: Don't take the sport you play for granted. Every time you play, you better be damn thankful that you get to do something you love. Don't show up to practice complaining about not wanting to be there; you're there hopefully because you love it," it said.

"Work hard every moment. If you're not working hard, you don't deserve to play. Play every practice or game like it's your last because it very well could be. When you finally reach the day that you can't play, and you can only watch, then you will know how much you love something that you once took for granted," he wrote.

The Colts Head coach Chuck Pagano commented on Mathis' injury on Monday.