Fletcher, 28, was ruled out of action indefinitely in December 2011 after being diagnosed with ulcerative colitis, a chronic bowel condition.
And, though Sir Alex is hopeful the Scotland captain's return to action will come sooner rather than later, he conceded that the player is still some way from making a recovery.
Speaking to MUTV, the 69-year-old Scot said: “We’ll wait and see about that [a comeback]. Obviously the boy is trying very hard to get back to his level.
"It’s not going to be easy but we’ll give him every possible chance and we’ll see how he does.
“He kept himself active towards the end of the season when he replaced Paul Scholes as Reserves coach when Scholes decided to come back to the fold.
“He’s a terrific lad and we all hope he can come back.”
Fletcher has made 302 appearances for the Red Devils since making his first-team debut in 2003.