The 25-year-old forward was stretchered off during the national team's defeat against Wales after just two minutes and now looks set for a prolonged spell on the sidelines
Martin O'Neill's side currently sit 15th in the Premier League, just four points above the relegation zone with eight games left to play, and Fletcher the club's top goalscorer with 11 goals in all competitions.
Having picked up his 12th international cap for Gordon Strachan's side against Wales on Friday before being stretchered off, Sunderland have confirmed Fletcher has returned to the club amid fears he may require surgery.
|BLACK CATS KEEP FALLING|
|11/4||Sunderland are 11/4 with BetVictor to be relegated this season|
Sunderland are without a victory in their last seven league games and host league leaders Manchester United on Saturday before a trip to Stamford Bridge to face Chelsea a week later.