ESPN College Football

After two years spent mostly watching from the sidelines, quarterback Cody Vaz gets the start for No. 10 Oregon State this Saturday when the Beavers travel to BYU.

It will be a challenging task for Vaz, who takes over after starter Sean Mannion injured his left knee against Washington State last weekend. Mannion had helped lead the Beavers to a 4-0 start and their highest ranking since the 2001 Fiesta Bowl season.

Vaz has appeared in only five games in his career, completing six of 17 passes for 48 yards. The 6-foot-1, 198-pound junior has not played in a game since the 2010 season.

He hasn't started since high school.

"I'm not really nervous, more so excited," Vaz said. "It's a great opportunity for our team. We're going into a tough place to play, a really good football team, a really good defensive team. It will be a great opportunity for us."

OK, really, no nerves?

"I can't wait," he said smiling. "I can't wait `til Saturday."

The question is whether Vaz can lead a team that has experienced a striking turnaround since finishing last season 3-9. Coach Mike Riley said he has complete confidence in Vaz, but does have one regret.

"The only unfortunate part is that I haven't played him enough," he said Tuesday.

Oregon State visits Provo to face an independent BYU team that is 4-2 but facing quarterback issues of its own. Cougars coach Bronco Mendenhall announced Monday that freshman quarterback Taysom Hill is out for the season after injuring his left knee in BYU's 6-3 victory over Utah State last Friday night.

Hill was standing in for senior quarterback Riley Nelson, who missed two games with what he described as "back fractures."

Nelson, who has thrown for 754 yards and five touchdowns with five interceptions, is expected to play against the Beavers on Saturday at LaVell Edwards Stadium.

Mendenhall learned of Oregon State's quarterback situation just before the start of practice on Monday.

"Who knows what the fallout is. You have a good offensive system in place that's very consistent from year to year. How that will be tailored all of a sudden to a new quarterback, I'm not certain," he said. "We'll prepare for what we know and then adjust to what we don't know or what we see on game day. That's really the best we can do."

Mannion's injury was a surprise, even to Riley. The 6-foot-5, 212-pound sophomore showed no sign of it during the Beavers' 19-6 victory over Washington State, when he was injured on a handoff but did not leave the game. He finished with 270 yards passing and a touchdown.

At 9:45 a.m. on Monday morning, just as the team was about to go into a meeting, the news hit.

"It was a total shock," Riley said. "The doctor and the trainer came running down the hall. So I knew it wasn't good."

Mannion is expected to have surgery to repair meniscus damage in his left knee as early as Wednesday. He will be week-to-week following the procedure.

Mannion was averaging 339.5 yards passing a game, second in the Pac-12 and sixth in the nation. He has thrown for 1,358 yards with seven touchdowns and four interceptions this season. He is sixth on Oregon State's career list with 4,686 yards.

A classic drop-back passer with a calm demeanor and a good grasp of the fundamentals, Mannion is the son of a high school football coach. He is one of four team captains for Oregon State this year.

Last season as a redshirt freshman, Mannion unseated junior starter Ryan Katz, who had started the 2010 season for the Beavers. Katz has since transferred to San Diego State.

Vaz grew up in Lodi, Calif., and played at St. Mary's High School, where he was 24-5 in two seasons as the starter. He was the Stockton Record's player of the year his senior season.

Vaz's backup going forward will be redshirt freshman quarterback Richie Harrington, a walk-on.

Oregon State has not opened a season 5-0 since 1939.