The 26-year-old was taken off at half-time during Saturday's goalless draw with Crystal Palace due to the recurrence of an ankle problem. He is expected to be sent for a scan to assess the severity of the damage and his manager Gus Poyet has his fingers crossed that the £12m forward does not face a lengthy lay-off. "We have to hope it is nothing serious," he admitted.
Fletcher spoke just last week about how he was desperate for a sustained period of football following a series of set-backs. "I haven't really had a run this season because of injuries, so it would be good to get one," he said.
The striker had only just recently returned to the side due to a niggling Achilles injury. Fletcher also dislocated his shoulder in September, just three games after returning from a six-month absence with an ankle ligament injury sustained on Scotland duty.
The forward, who played the first 45 minutes in the recent friendly win over Poland, has been struggling for form this season, and has only scored three goals in 25 appearances for Sunderland so far.