Fletcher takes 'extended break' from football
United revealed that Fletcher, who has been sidelined at various points in recent times with what was reported to be a virus, has been suffering with the condition for some time.
The 27-year-old has now been advised to take a complete break from the game. The club said in a statement: "On behalf of Darren Fletcher, Manchester United wishes to announce that he is taking an extended break from football for health reasons."
Fletcher made only one start for United last season after 1 March, and was an unused substitute for the 3-1 UEFA Champions League final defeat by Barcelona.
He has made ten appearances in all competitions for the Red Devils during the current campaign, with the last coming on 22 November.
The statement from United continued: "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."
Levein concerned for 'inspirational' captain
Fletcher, the Scotland captain, has also played for his country in four UEFA EURO 2012 qualifiers this season.
Scotland manager Craig Levein said: "I am obviously absolutely devastated for Darren because I know how hard he has worked to get back to playing regularly for his club and country.
"He is one of the most inspirational players I have had the pleasure of working with and on behalf of his Scotland team-mates and my backroom staff I sincerely hope this time off, allied to the support of his family, will enable him to make a full recovery.
"I spoke with Sir Alex Ferguson and Darren this week and the most important thing at this stage is for the player to be given time to rest and recuperate.
"Nobody is more committed to his country's cause than our captain. He is a central part of our plans for the World Cup 2014 qualifiers but at this stage his health is paramount and I would like to reiterate the best wishes of everyone involved with the national team and the Scottish FA."