Sunderland are awaiting the results of scans on an ankle injury suffered by top scorer Steven Fletcher on international duty last week.
Fletcher, 25, who has struck 11 times for the Wearsiders this season, had to be stretchered off as the Scots lost 2-1 to Wales in a World Cup qualifier at Hampden on Friday.
Sunderland said their medical team were assessing Fletcher, who suffered the injury when he landed awkwardly after only two minutes of the match.
A statement on the club's official website explained: "Steven Fletcher has returned to Wearside after picking up an injury with Scotland.
"Fletcher is currently being assessed by the club's medical team and is awaiting scan results to find out the extent of his injury.''
Fletcher was signed by Sunderland for £12 million from Wolves and his absence would be a major blow for Martin O'Neill's side, who are four points clear of the relegation zone and struggling for goals.