In his first four games this year, Mannion completed 63.3 percent of his passes for 1,358 yards, seven touchdowns and four interceptions (three of which came last week against Washington State).
Meanwhile, BYU is getting its original starting quarterback – Riley Nelson – back.
"Riley's doing good," said Coach Mendenhall after Tuesday's practice. "He looks close to normal, and I'm confident. I like the way he's running around, I like the way he's throwing. [He looked] better today than yesterday."
Nelson accounted for 306 total yards and three touchdowns last year against an OSU team that ended up only winning three games, but this Saturday should be a much stiffer test and should be lower scoring.
As for the Beavers' offense, they will be featuring junior Cody Vaz at quarterback in Mannion's absence. Vaz hasn't played since 2010 and has never started a college game. As a college quarterback, he has completed 6-of-17 passes for 48 yards, no touchdowns and no interceptions.
Given his lack of playing time, scouting him out is a difficult task.
"It's not really possible," said Mendenhall. "You can go back to high school film. He played against Stanford in 2010. There's spring games, etc., but their offense is their offense and to make drastic changes in one week, [I don't expect that]. They have good players all around him, so their comments as coaches are that they have a lot of confidence [in him], he's a quick decision-maker and a good leader. So my guess is that they'll be similar, but we'll have to adjust if they're not."
Given that BYU's defense is currently fifth in the nation in total defense and third in scoring defense, and that the Cougars will have the home field advantage, that doesn't bode well for OSU. However, Mendenhall doesn't think that the circumstances mean the game will be easy.
"It will still be formidable no matter who's playing quarterback for them," he said. "They're a good team and I think that's why they're voted [10th], and they're undefeated and it's not easy to do that, so they'll be good enough."
Helping Vaz out will be OSU's two leading receivers in Markus Wheaton and Brandin Cooks, who have combined for 62 catches for 984 yards and six touchdowns so far this year. Last year against BYU, the two combined for 11 catches for 194 yards and one touchdown.
"They're fast and quick and really good after the catch," Mendenhall said about the Beaver receivers.
He noted that OSU likes to utilize a lot of quick throws, but will also have a lot of deep throws as well.
While Oregon State is tied for eighth in the nation with 339.50 passing yards per game, the team is also only 103rd in the nation with 118.50 rushing yards per game.
Their rushing total may be deceiving, however.
"I think they run it effectively, they've just chosen – with the receivers they have – to throw it for about 340 a game and run it for about 120," said Mendenhall. "And so it's not because of lack of talent. They run it well when they choose to, but they have such good weapons on the outside and had such a nice throwing quarterback, they could score more points that way. So what they do this week, I'm not sure, but the scheme is good enough to carry them if they want to do that, I think."
Mendenhall also gushed about OSU head coach Mike Riley.
When asked about why he thinks Riley has been so successful at OSU, Mendenhall replied, "Because he's a great person and a really good coach, and he has the right values and he's very consistent and he's surrounded himself with the right coaches. He has the right perspective and he's a great fit for that community, and I hope he stays there forever if he wants to. He's a really good man and a good coach."