Oregon State quarterback Sean Mannion is out indefinitely after injuring his left knee during the No. 10 Beavers' victory over Washington State on Saturday.
Backup Cody Vaz will start for the undefeated Beavers when they play a nonconference game against BYU this weekend.
Mannion had his knee in a brace at practice on Monday. Coach Mike Riley says an MRI has indicated the sophomore quarterback will require surgery.
Mannion threw for 270 yards and a touchdown in Oregon State's 19-6 victory over the Cougars. He apparently injured the knee on a handoff but did not leave the game.