SAN DIEGO -- The San Diego Chargers say running back Ryan Mathews has a sprained medial collateral ligament in his right knee.
Coach Mike McCoy won't say how much time Mathews is expected to miss, other than "he'll be out for a little bit of time.''
McCoy says every player heals differently and "I don't want to put a timetable on anything.''
According to ESPN's Adam Caplan and multiple reports, Mathews suffered what is believed to be a grade-2 right MCL sprain (partial tear), which is expected to keep him out four weeks.
Mathews was taken off the field on a cart Sunday after hurting his knee trying to recover his own fumble in the fourth quarter of a 30-21 victory against the Seattle Seahawks.
Mathews is in the final year of his contract. Last year was the first time he played all 16 regular-season games. He gained a career-high 1,255 yards.
The Chargers (1-1) have Danny Woodhead, Donald Brown and rookie Branden Oliver at running back.
"Donald's played a ton of football," McCoy said. "The number of snaps he got in Indy in a very similar system, when he was with Peyton [Manning], so coming here we knew exactly what he can do. We've got a lot of confidence in him. We've said that we're going to play all our backs, certain rotations, certain number of plays. Some weeks it's going to be more than others and it's the second week in and they'll take a few more snaps. We have confidence in all our players. That's why they're here."
The Associated Press contributed to this report.