Hanson was on his way to the club's spring training camp in Florida on Monday when a tire blew out on his vehicle. He may have hit his head on the steering wheel, Braves manager Fredi Gonzalez said.
Gonzalez said Tuesday that doctors diagnosed Hanson with a mild concussion, which will keep him out of workouts for a couple of days. He will then be evaluated again.
Hanson was 11-7 with a 3.60 earned run average in 22 starts last season, but missed most of the final two months because of shoulder problems.