Illinois junior quarterback Nathan Scheelhaase practiced Wednesday and is questionable for Saturday's game against Arizona State due to an ankle injury, according to coach Tim Beckman.
"(Scheelhaase) practiced today, so we'll see how he responds," Beckman said on Wednesday. "He's much better than he was yesterday.
"He said he felt pretty good. I think anytime you have an injury to the ankle it's going to progress. It's been progressing, and we're going to have to make that decision on Thursday after practice."
Scheelhaase left Saturday's game against Western Michigan late in the third quarter with the ankle injury.
A three-year starter, Scheelhaase was 11 of 18 for 126 yards, a touchdown and an interception in the 24-7 win over Western Michigan. He also rushed for 21 yards and one touchdown.
O'Toole replaced Scheelhaase against Western Michigan and completed 2 of 3 passes for 7 yards. He was 40 of 67 for 240 yards, one touchdown and four interceptions as a freshman.
Osei is 1 of 2 for 3 yards in his career and has appeared in 14 games the past two seasons.
"I thought Reilly and Miles are probably neck and neck right now to determine on who the starting quarterback is going to be for us on Thursday, and we'll see how Nathan progresses," Beckman said. "Of course, Nathan hasn't had the number of reps. Reilly and Miles, they've both had reps with the ones. We'll make the decision on Thursday."
Illinois defeated Arizona State 17-14 in Champaign, Ill., last season. Scheelhaase was 11 of 15 for 135 yards, a touchdown and an interception and rushed for a team-high 67 yards.
Both teams enter this season's game coming off wins in their opener.