Iowa quarterback Cade McNamara is out for this week's game against Wisconsin after leaving Saturday's win against Northwestern with a concussion.
Hawkeyes coach Kirk Ferentz confirmed the injury Tuesday.
Brendan Sullivan, a transfer from Northwestern, replaced McNamara in the second quarter on Saturday and is listed as the starter. Redshirt freshman Marco Lainez will be the backup.
Ferentz said he was hopeful McNamara would return to face UCLA on Nov. 8.
Sullivan had 79 passing yards and 41 rushing yards and a touchdown against the Wildcats. On Saturday, Ferentz cautioned against the change being permanent, saying they planned to play both quarterbacks. Ferentz said McNamara took a hard hit before being removed from the game and was "shook up, hit the turf pretty hard."
McNamara had an interception returned for a touchdown shortly before being removed from the game. He appeared on the sideline without his helmet in the second half.
The transfer from Michigan has battled injuries throughout his time at Iowa but opened the past two seasons as the team's starter. He has 1,017 passing yards with six touchdowns and five interceptions this season.
"Feel badly for him because it's been a tough stretch really for about two and a half years," Ferentz said. "I've said it before and you guys have heard me say it a million times -- the worst thing about coaching is dealing with injuries. It's something nobody wants to deal with, and certainly he's had his tough share of bad luck here. I feel bad about that, but hopefully we'll get him back soon, get him back on his feet."