Notre Dame senior defensive lineman Ian Williams tore the medial collateral ligament in his left knee and will miss four to six weeks, possibly ending his regular season, a source close to the player said Monday.
Williams was one of Notre Dame's most consistent defensive players with 37 tackles, leading all defensive linemen.
Notre Dame has four games over the next five weeks and is 4-4.
Williams was injured in the second half of a loss to Navy on Saturday. It is possible Williams may be able to return for a game against USC or a bowl game. Either way, Williams hopes to participate in this year's Senior Bowl.
Joe Schad is a college football reporter for ESPN.com.