"People who talk like that are badly informed," the United striker has told the News Of The World.
"They hear things said and they speculate. I had six pieces of cartilage in my knee. Was that psychological?
"It has happened that I take part in training in the week, feel good and then declare myself unfit for the weekend.
"But there's an explanation. My knee could hold up for 20 minutes in training but would never have done so with the intensity of a 90-minute match. It would have been ridiculous to play at less than 100 per cent.
"I have never refused to play. Each time I have missed a match, it was because I could not play.
"Bad luck does not explain everything. Repeated matches wear on the body. My game is based on speed, requiring rapid changes of direction and push-offs.
"That demands a lot of the body and it's a vicious circle. I suffered with my left knee and in compensating, the right one went.
"Now I am doing all I can to avoid another set-back - acupuncture, physiotherapy, osteopathy. It is beginning to pay off. What I'd like now is a goal. That would help me."