Fletcher in bowel condition battle
The Scotland international has surprised himself with the progress he has made so far this season after being kept out of football for 10 months with the problem.
Fletcher, 28, has made four senior appearances this term and believes that his experience has helped him to make a swift return to United's first team.
"The condition never goes away and that's the thing I have to live with," Fletcher told reporters.
"Every day is a battle for me. I have to watch my diet and take certain medication or it could come back again.
"But I am back quicker than I expected. It has been a lot quicker, but that maybe comes down to experience.
"Maybe you don’t have the sharpness in your legs yet, but it is in your mind, where you can react quicker because you have been in the situations before.
"I think my legs are coming back. If you had said I would be in this position back in June and July, I wouldn't have believed you, but as I am here now I think it is going well."
Fletcher returned to United's first team against Galatasaray in the Champions League in September.
The midfielder said that manager Sir Alex Ferguson's caution caused him to delay his comeback to the senior squad.
"I was impatient but the manager told me I had to be patient," Fletcher said.
"When you have been out for a long time you are desperate to play so maybe you do push yourself, but I had good people around me like the sports science staff, the manager and the reserve manager Warren Joyce.
"They were there with the reins on me, holding me back. Deep down, I always knew they were right but it is hard to accept because you are desperate to get back as quickly as possible.
"I feel great, but when you have been out for a long time it is going to take time before you are 100 per cent."