Dennis Wise said: "Leon will be out for a couple of months. He fell after he'd scored and the break was so severe he shouldn't have carried on. He's had a plate in his arm and it will be two months."
Wise's injury list is getting bigger with midfielder Jonathon Douglas (knee ligament damage), fellow midfielder Alan Thompson (hamstring), Jonny Howson (knee), Ben Parker (foot) and Radostin Kishishev (a knock).
Centre-half Matt Heath is also out of Saturday's home match with Northampton due to suspension.