Sean Mannion will start at quarterback for Oregon State on Saturday against Cal, replacing injured Cody Vaz.
Vaz went down in last Saturday's Pac-12 loss against Stanford with an ankle injury. Coach Mike Riley said Vaz is expected to be in uniform Saturday but gave no indication whether he would be able to play.
Mannion suffered a knee injury after starting the Beavers' first four games this season. He returned after sitting out two games but threw four interceptions against Washington and was benched in favor of Vaz, who has started four of the past five games.
Oregon State (7-2, 5-2 Pac-12) has lost two of its past three games and has fallen to No. 16 in the BCS standings.