The Scotland international has been battling illness for the past year, and has now decided to take a rest from training and matches as he seeks a return to full fitness
Fletcher, 27, has managed only 10 appearances this season for the Premier League champions after failing to recover from a mysterious illness picked up towards the end of 2010.
The Scotland international has now decided that further action is required if he is to regain his fitness, and has therefore taken an extended leave of absence from the game.
A statement on the club’s official website read: “On behalf of Darren Fletcher, Manchester United wishes to announce that he is taking an extended break from football for health reasons.
“Over the past year he has had several absence periods which we have attributed to a viral illness in order to respect his right to medical confidentiality. Darren has, in fact, been suffering from ulcerative colitis (a chronic inflammatory bowel condition) for some time preceding this.
“Whilst he was able to maintain remission of symptoms for a considerable period this has proved more difficult recently and Darren’s continued desire to play and his loyalty to both his club and country has probably compromised the chances of optimising his own health and fitness.
“He has therefore accepted medical advice to take an extended break from the demands of training and playing in order to afford the best chance possible of achieving full remission once again.
“We request that his privacy is respected and hope that the removal of the additional stress associated with speculation regarding his health will also aid his recovery.”
The news will come as a blow to Sir Alex Ferguson, who has already lost central midfielders Tom Cleverley and Anderson to injury until the New Year.
This latest blow may force the 69-year-old to delve in to the transfer kitty in January in a bid to sure up the spine of his side, which will also be without captain Nemanja Vidic for the rest of the season.