The Scottish midfielder came on in the 70th minute to replace Ryan Giggs - his first senior appearance in the Premier League since Boxing Day last year - and manager David Moyes was delighted to see him back.
"If anybody returns from an illness to play professional football on this kind of stage for a club like Manchester United, it shows a lot about the boy himself," said Moyes.
"He has had to be on his own, he has been in and out of hospital, he has had operations.
"Today was a big message to a lot of people - keep believing.
"If you are not well then keep believing that you can get yourself right."
The day ended well for Fletcher with United posting a 3-0 win over Aston Villa at Villa Park to move up to eighth on the league table.
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