The midfielder has not played since November 22 due to a condition known as ulcerative colitis, a form of inflammatory bowel disease.
Fletcher, 27, is still to return to training and has instead taken over some of the coaching responsibilities Paul Scholes abandoned when he came out of retirement.
There is still no precise date for when Fletcher will step up his recovery programme.
"I'm still not ready to come back playing or training yet but I'm listening to the medical people and trying to get myself right," Fletcher told BBC Scotland's Sportscene programme. "The challenge and the focus is to be ready for next season.
"Me and the medical team decided it'd be best if I tried to get myself right and take an extended period out from the game; then come back fully fit and ready to play."