Senior Reilly O'Toole, who played limited snaps in each of the Illini's previous four games, made the third start of his career and first since 2012.
Illini spokesman Kent Brown said Lunt hurt his leg in last week's game against Texas State. Lunt was in uniform and went through pregame warm-ups. The nature of his injury wasn't disclosed, but Brown said he was held out because of a mobility issue.
Lunt, a sophomore transfer from Oklahoma State, is the Big Ten's No. 2 passer - at 309 yards per game - and leads the conference with 11 touchdown passes.