FILE - This is a July 3, 2014, file photo showing Robert Mathis of the Indianapolis Colts NFL football team. A person with knowledge of the injury tells The Associated Press that Mathis is expected to miss the entire season after tearing an Achilles tendon during a private workout last week in Atlanta. The person spoke Monday, Sept. 8, 2014, on condition of anonymity because the team had not confirmed Mathis' injury. (AP Photo/File)
FILE - From left are 2014, file photos showing NFL football players Aldon Smith, Josh Gordon and Robert Mathis. A solid trio to put on any NFL field. Except that they are among the players suspended by the league heading into the 2014 season. (AP Photo/File)
INDIANAPOLIS — Robert Mathis likely won't get a chance to defend his NFL sacks title.
Less than two weeks after starting a four-game, league-imposed suspension, the Colts' best pass rusher sustained an Achilles' tendon injury while working out privately in Atlanta.
A person with knowledge of the injury told The Associated Press on Monday that Mathis tore the tendon, which would keep him out the entire season. The person spoke on condition of anonymity because the team has not confirmed the diagnosis.
A few hours later, coach Chuck Pagano said he would not speculate on the severity of the injury or how much time Mathis could miss — until team doctors examine Mathis on Tuesday. But it sure didn't sound promising.
"We knew we were going to be without Robert for the first four games, but this is really a devastating blow for Robert and his family and this organization," Pagano said. "This one stings."
The injury occurred while Mathis was away from the team, serving his suspension.
League rules prohibit Mathis from working out at the team complex or communicating with those inside the organization during his absence, so the Colts sent Mathis home with a workout regimen.
On Monday, Mathis contacted head trainer Dave Hammer to inform the team that he had injured the Achilles and had already been seen by one doctor.
Pagano said league rules do allow suspended players to contact their team if they are injured.
Mathis' teammates were then told of the injury during Monday's team meeting and the news hit hard.
"He's a pillar guy," inside linebacker Jerrell Freeman said with uncharacteristic somberness. "He's definitely a leader and I hope he'll be on the sideline coaching when he gets back."
But it's also another odd twist in what had already been a tumultuous season for the Colts' career sacks leader.
In May, NFL officials announced Mathis would be suspended for the first four regular-season games after violating the league's performance-enhancing substance policy.
Mathis claimed he was taking a fertility drug, Clomid, so he and his wife could have another child. But the drug is on the league's banned list because it can be used as a masking agent for PEDs.
Mathis grudgingly accepted his fate after his appeals were denied.
Critics contended that the substance explained Mathis' sudden statistical surge last season, when at the age of 32 he set a single-season franchise record with 19 1/2 sacks and won his first NFL sacks crown. Mathis argued he was more comfortable playing his new position, outside linebacker, after converting from defensive end in 2012.
And also he was motivated to perform even better after some thought his numbers would drop significantly after longtime friend Dwight Freeney signed with San Diego.
At training camp, the 6-foot-2, 245-pound Mathis was frequently seen playing with his newborn daughter following practice, and even though Pagano acknowledged the Colts needed Mathis to get some work before the suspension, Indianapolis held him out of all four preseason games.
Before departing the team complex Aug. 30, Mathis left an inspirational note in his locker urging players and coaches not to take the game they love for granted. Defensive end Cory Redding explained it was simply "Robert being Robert," a message that resonated throughout the team.
"I don't want to talk about another man's injury issues, medical issues, but, I do know I love Robert," Andrew Luck said. "He doesn't know how much he has meant to me as a rookie, second-year guy, offseason, everything.
"What he's done for this organization, what he will continue to do for this organization I know is going to be special."
So the Colts (0-1) must now figure out how to cope without their best pass rusher.
A year ago, Mathis' teammates combined for 22 1/2 sacks.
On Sunday night at Denver, it was obvious how much Indianapolis missed Mathis.
Indy struggled to consistently pressure Peyton Manning and wound up with only one sack, and Bjoern Werner, Mathis' replacement as the rush linebacker, had three tackles but no quarterback pressures. They host the up-tempo Eagles next Monday night.
"You can't replace a guy like Robert," inside linebacker D'Qwell Jackson said. "But we trust our guys, we trust the guys next to us."
Mathis is the second Indy player to sustain an Achilles tendon injury this season, joining running back Vick Ballard who is already on injured reserve after tearing his left Achilles in late July.
Indy already has 10 players on injured reserve, including offensive lineman Xavier Nixon, who was designated for a possible return later this season.
"It's a tough, tough pill to swallow and they're just absorbing it right now, the shock of it all," Pagano said. "Like Reggie (Wayne), I know he'll get through it with whatever he has to do and he'll be back."
Notes: Wayne had nine catches for 98 yards in his first game back after tearing the ACL in his right knee. ... Freeman (hamstring, thumb) said he felt fine Monday and expected to play next week. ... Luck blamed himself for calling a quarterback sneak on fourth-and-goal, which resulted in a Denver stop. Luck called it "stupid" decision.