Sunderland manager Steve Bruce is concerned that striker Fraizer Campbell may have suffered a serious knee injury in the 1-0 home win over Manchester City.
Campbell had to be replaced by Danny Welbeck at half-time, with defender Michael Turner also being forced off due to an ankle problem.
Bruce told his club's official website:"Michael Turner's hurt his ankle, but I have to say we're frightened about Fraizer's injury.
"He's twisted his knee ligaments, but we won't know until we scan him. We hope he is going to be okay because in that area we are light.
"He could be out for an extended length of time and that would be a big blow for us."
Of his side's tense victory, Bruce added:"Man for man it was all about what the Premier League is. We passed it well, but the great thing is everyone stuck at their jobs and it was good to see us being resolute.
"There's been a lot of negativity around the place. Now we have to make sure we keep moving forward and results like this obviously help."