The Scotland international missed two months at the end of last term and the club’s pre-season trip to North America due to the illness, before returning to action.
However, the Premier League champions have revealed that Fletcher will be given time to return to health before training or playing again.
“On behalf of Darren Fletcher, Manchester United wishes to announce that he is taking an extended break from football for health reasons,” a United statement reads.
“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,” it concluded.
The news will be a blow for Sir Alex Ferguson’s men, who are already without Anderson and Tom Cleverley due to injury.
By Gareth McKnight