The Scottish midfielder lost almost two years of his career due to the inflammatory bowel condition - he made only 10 appearances in each of the 2011/12 and 2012/13 seasons.
But after returning against Aston Villa in mid-December and successfully establishing himself in David Moyes' plans, Fletcher has been speaking honestly and emotionally about the troubles he experienced during his time away from football.
On Wednesday he joined forces with a fellow sufferer in sport, the rugby legend Lewis Moody, to launch United for Colitis - a new fundraising initiative for the Crohn's and Colitis UK charity.
"The big thing is awareness," said Fletcher. "When I was first diagnosed, I was blasé about it, which was quite immature. I was a professional footballer at Manchester United. I felt untouchable.
"I want people to take ulcerative colitis seriously and understand what it can lead to and what an impact it can have on their lives.
"I started my real battle with it in 2010 and ultimately I had to have surgery so I could continue my career. But I stayed silent about it until 2011.