Fletcher 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.''
Source: Sunderland-Mad
Source: FOOTYMAD
