The midfielder began an extended break from football in December after suffering from ulcerative colitis, a chronic bowel condition.
The 28-year-old, will see his usual team of specialists next month and sources at Old Trafford say the club are optimistic that he will get the all-clear to start pre-season training in July.
Earlier this year, there were rumours that the Scot may be forced to retire from football but having played his last game against Benfica in November.
But United manager Sir Alex Ferguson has spoken of his hope that Fletcher, who is under contract until 2015, will return to action.
"We're hoping he will start pre-season training,” Sir Alex said earlier this month.
"But we can't assess it because we don't know enough about it.
"Darren's medical people are dealing with it and our doctor has a good idea of the situation but at the moment the boy is doing his best to come back."