UCLA middle linebacker Patrick Larimore won't play this season, leaving a gaping hole in the center of the Bruins' defense.
Larimore will "medically retire" from football, according to the Los Angeles Daily News.
He had a recurrence of concussion-related symptoms Tuesday and missed practice. It was his second concussion in six months.
Larimore emerged as a game-changer in the middle as a sophomore, when he unseated Patrick Sloan. He was UCLA's defensive MVP in 2012, leading the Bruins with 81 tackles.
The Bruins lost offensive guard Chris Ward (knee, ankle) to medical retirement last week.