Roberson, a sophomore from Newbury Park, Calif., was on the scout team last season as a freshman. He tore his lateral collateral ligament and partially tore an anterior cruciate ligament on Saturday. He was supposed to provide depth to Cierre Wood and Jonas Gray.
Linebacker Anthony McDonald has a partially torn pectoral muscle but should be ready for the start of August preseason camp, the school said Wednesday. His injury will also require surgery.
McDonald, a senior from Burbank, Calif., is expected to compete for playing time. McDonald was on his way to being a starter at inside linebacker a year ago before hurting his knee in preseason practice, and the job eventually went to Carlo Calabrese.
The Irish added two freshman walk-ons: running back Tyler Platz of New Lennox, Ill., and wide receiver Ryan Liebscher of Colorado Springs, Colo.