Sir Alex Ferguson ruled the England squad member out of action until Christmas after he suffered a recurrence of the problem during the win at Everton. However, Fletcher is convinced Cleverley will return to play a key role this term.
"It is disappointing," conceded the Scot. "Tom will be very disappointed personally, as we are as a team. He had been performing so well and had a great start to the season. The important thing now is that he gets the injury right. It is one of those niggly ones. He came back and had a recurrence.
"The best thing for him to do is get himself right. He will be an important player for the remainder of the season and hopefully the push for silverware. He is thought very highly of and rightly so because of his performances. People say he is still young but he has had a lot of experience. He was in the [Barclays] Premier League with Wigan last year and had a loan spell at Watford.
"He did fantastically well at both clubs. We are delighted to have him back from Wigan. He is an important part of our squad now and has fought his way into the team with some great performances this season."