ASHBURN, Va. -- Washington Commanders rookie defensive tackle Phidarian Mathis suffered a season-ending knee injury Sunday after further tests confirmed what the team feared after the game, according to a source.
Mathis, a second-round pick in April, tore his left meniscus when he was blocked into where the ball carrier was being tackled and had his knee bent during Washington's 28-22 win over the Jacksonville Jaguars on Sunday.
His injury left Washington thin at defensive tackle behind starters Daron Payne and Jon Allen. Those two played 55 and 54 snaps, respectively; Jacksonville ran 62 plays. Washington coach Ron Rivera said the team would likely sign another defensive tackle to the active roster and possibly add another to the practice squad.
"You don't want those tackles to play as much as they did," Rivera said.
Rivera said Sunday night he was concerned about the severity of Mathis' injury, so Monday's test results did not surprise him.
The Commanders placed Mathis on injured reserve later on Monday and signed defensive tackle Donovan Jeter in a corresponding move.
Washington drafted Mathis with the 47th overall pick to rebuild its depth along its interior defensive line. The Commanders cut Matt Ioannidis in March and lost Tim Settle to free agency. They liked Mathis in part because he could play more as a nose, a job usually reserved for Payne. The Commanders hoped it would free Payne to play more of the 3-technique when they were paired in pass-rush situations.
"It's tough whenever you have a young guy like that go down so early in the season," Allen said. "It's unfortunate. For us, we're going to be fine. We've been through this before. We have players who are going to step up and play well. And, for me, it's just I feel bad for him having to go out so early in his career."
Allen underwent an MRI on his groin, but he called it precautionary and that there was nothing to worry about.
The NFL Network first reported the extent of Mathis' injury.