Last season, Miller sprained a knee early against San Diego State and missed the rest of that game and the next two, with Guiton filling in.
Then Miller partially tore the labrum in his right shoulder on the first possession against Clemson in the Orange Bowl. He played the rest of the game. When the injury was discovered later, he had surgery in February.
Ohio State said at the time that Miller had "minor, outpatient surgery." But he has had problems with the shoulder since.
Still, he has repeatedly said he would be ready to go in the opener and did so again between practices Monday. His workload had been reduced to avoid any ongoing soreness in the arm.
Miller has a $1 million total disability policy that he could collect if he never plays football again, a source told ESPN. That premium has been paid for by Ohio State, according to the source, but Miller does not have loss of value insurance that would cover him if he significantly slipped in the NFL draft.
ESPN.com's Austin Ward, ESPN's Darren Rovell and The Associated Press contributed to this report.