The Scotland midfielder has already begun his coaching badges, preparing for a career he had hoped was a long time off.
But now the spectre of retirement is looming after Ferguson painted a bleak picture of the 28-year-old's fight to combat a chronic bowel complaint that has been bothering Fletcher since March 2011 and forced him to take a full break from the game last November. He said: "Darren has not started training with us."
He added: "Obviously he has got challenges and we are happy to be patient with him.
"But he won't be starting the season.
"It is unfortunate because he is such a magnificent professional and such a nice lad.
"If it doesn't work for him he knows he has a position at the club."
Fletcher was restricted to just 10 appearances last term, his last coming against Benfica at Old Trafford in November.
He turned out just twice in the final weeks of the previous campaign, when the 'virus' first took hold, costing him a chance of finally appearing in a Champions League final, after he was overlooked for the 2008 triumph over Chelsea in Moscow and then suspended the following year, when United lost to Barcelona.