Stephane Sessegnon has picked up an ankle injury that could make him a doubt for Sunderland's final pre-season game against Leicester City on Saturday.
Sessegnon, 28, had an extended summer break due to his involvement in World Cup qualifiers in June. He suffered the injury in training and has been forced to miss Wednesday's friendly against Derby County at Pride Park.
He has undergone a scan to assess the damage, and Sunderland manager Martin O'Neill said he is waiting on news of whether he will be fit to play at the weekend.
"Sessegnon hurt his ankle in training on Monday and I don't know whether he will make tonight's game," he added. "Hopefully he will be OK for Saturday's match."
O'Neill, who has so far signed only defender Carlos Cuellar, released by Aston Villa at the end of last season , also has other injury concerns ahead of the new season.
He revealed: "[Ahmed] Elmohamady is back and not doing too badly, so he should be in action. We'll see. We've got a couple of injuries to contend with.
"Phil [Bardsley] has had a setback too, which is a shame, but whatever comes and goes we'll have to get ourselves ready for Saturday week and the start of the new season."
Meanwhile, Wolves have denied accepting a £12 million Sunderland bid for Scotland striker Steven Fletcher.
Molineux chief executive Jez Moxey told the Express and Star: "Rumours that we have accepted a bid from Sunderland are incorrect. They want the player, but we haven't accepted anything."
It is believed he two clubs are still talking about a possible deal for Fletcher, 25, who is O'Neill's main transfer target of the summer.
But Moxey has said Wolves want to keep all their key players as they target an immediate return to the top flight following last season's relegation.