USC defensive end Leonard Williams, the Trojans' leading tackler, is "very questionable" for Saturday's game at California because of a shoulder injury, interim Coach Ed Orgeron said.
Williams was injured during USC's victory over Oregon State last week. He returned to practice Thursday after sitting out two days to receive rehabilitation treatment.
Williams, however, did not participate in all drills.
Williams has 56 tackles. He also has a team-best 11 tackles for loss, including five sacks.
J.R. Tavai has played linebacker the last few games, but he could return to end if Williams is unavailable.
USC is 6-3 overall and 3-2 in the Pac-12 Conference. Cal is 1-8 and 0-6 in the Pac-12.