The Scotland international has not featured in the team since November due to a chronic bowel complaint and United said at the end of last year that he would be out of the game for an indefinite period.
Recently though there had been reports that he was making excellent progress and he could possibly return to the side before the end of the campaign.
Those hopes have been quashed by Sir Alex Ferguson.
"I don't expect Fletcher to come back," said the United boss. "Darren will be out for the season."