Sunderland boss O'Neill told The Sun: "I don't know if we will see James in the team any time soon because on Thursday he pulled up with a hamstring.
"I hope it is not too serious, but he was certainly feeling it. So that is a setback. It is a real shame because James has worked exceptionally hard on his fitness and was enjoying the training.
"He needs to have a chance and I hope the hamstring is not too serious. You have to remember he did not play often for Everton last season."
McFadden's contract at Sunderland runs out in January.