Sunderland are anxiously awaiting news on Lee Cattermole after the midfielder limped out of a pre-season friendly on Saturday.
Cattermole, who made just 19 Premier League appearances for the Black Cats last season following heel and knee injuries, lasted less than 30 minutes of Saturday's game against Darlington.
Sunderland won the friendly 1-0 following a late goal from Bolo Zenden.
The 22-year-old had been expected to miss the game at the Northern Echo Arena after appearing to pick up the injury during an outing against Munster earlier in the week.
"Lee wanted to try it out but he suffered a recurrence after ten minutes," explained assistant manager Eric Black.
"We may now send him to see a specialist on Monday."