CORVALLIS, Ore. -- 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 6-foot-5, 212-pound sophomore quarterback will require surgery.
The specific nature of Mannion's injury was not released.
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.
More: Beavers defeat WSU
Following the victory, Oregon State jumped into the Top 10 of the AP rankings for the first time since 2001, when the Beavers went to the Fiesta Bowl.
Mannion was averaging 339.5 yards passing a game, second in the Pac-12 and sixth in the nation.
Mannion has thrown for 1,358 yards with seven touchdowns and four interceptions this season.
Vaz, a 6-foot-1, 198-pound junior, played in five games in the 2010 season, completing six of 17 passes for 48 yards. He did not appear in any games last season for the Beavers.