Notre Dame lost one of its key defensive players for the year.
Irish senior defensive end Kapron Lewis-Moore will not play the rest of the season after suffering a right knee injury in Saturday night's loss to USC, coach Brian Kelly said Tuesday.
Lewis-Moore started the first seven games and has 26 tackles with four tackles for loss.
"It was a very unusual injury. Our doctors couldn't really get a good feel after the game for what it was. He had stability in his knee," Kelly said. "He actually detached the medial collateral ligament, didn't tear it, he detached it."
Kelly said the injury will be treated like a torn anterior cruciate ligament and will take four to six months for Lewis-Moore to heal.
"(The injury) is one that I haven't seen in 21 years, and our doctors have seen very rarely," Kelly said.
Lewis-Moore with be replaced by freshman Stephon Tuitt in the starting lineup, and freshman Chase Hounshell is listed as the No. 2 end behind Tuitt.
Senior defensive end Ethan Johnson is expected to return this week after missing the last two games with a high right ankle sprain.
But Kelly said he doubts Johnson will be able to resume a full work load, which leaves Notre Dame (4-3) with a young group of defensive linemen as it plays host to Navy (2-5) on Saturday.
Freshman Aaron Lynch could start for a third straight game in front of Johnson at defensive end, and sophomore nose guard Louis Nix will only be playing his eighth game Saturday.
"Kapron and Ethan have more experience against the option than anybody here in terms of actually understanding their jobs and what to do," Kelly said. "But we'll call on the next guy."
Kelly did have some positive news about players who suffered injuries in the loss to USC.
Quarterback Tommy Rees, who injured his knee but was able to return against the Trojans, and safety Zeke Motta, who suffered a concussion, are both cleared to play, Kelly said.