The 25-year-old has returned to the Barclays Premier League side and is being assessed by the Sunderland medical team, the club confirmed on Monday.
A statement on Sunderland's official website said: "Sunderland's 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."
The £12million centre-forward has been one of the Black Cats' most dangerous attacking options, and if he is ruled out for the rest of the season manager Martin O'Neill would be heavily reliant on January signing Danny Graham, who is yet to score after six appearances.
Fletcher has scored 11 goals for Sunderland since he joined the club from Wolves last summer.
O'Neill's side are currently four points above the relegation zone.
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