USC freshman quarterback Jaxson Dart had surgery to repair a meniscus injury and will be out indefinitely, a source confirmed to ESPN on Thursday.
Three-year starter Kedon Slovis is expected to start against Oregon State on Saturday.
Dart replaced Slovis during the Trojans' 45-14 win at Washington State last Saturday after Slovis was knocked out of the game during the opening drive because of a neck injury.
Dart came off the bench to throw for 391 yards and four touchdowns but injured his right knee in the second quarter. The Kaysville, Utah, native played the second half with a heavy sleeve on it and had a noticeable limp at times.
Interim coach Donte Williams did not discuss Dart's status on Tuesday, only noting that he was not available to practice.
The strong showing from Dart raised the possibility that Slovis could be benched for the first time because of poor play. He has started all but one game since taking over when J.T. Daniels sustained a knee injury in the 2019 season opener, missing the game at Washington that year after sustaining a concussion.
The offense was sluggish in USC's first two games this season, managing 23 points in a win over San Jose State before being thumped in a 42-28 loss to Stanford that marked the final game of Clay Helton's roller-coaster tenure. Slovis directed two late touchdown drives against the Cardinal after the outcome was decided.
Slovis has thrown for 487 yards and three touchdowns with one interception, completing 65% of his passes in three games this season.
24/7 Sports first reported that Dart underwent knee surgery.
Information from ESPN's Kyle Bonagura and the Associated Press was used in this report.