Wayne Rooney is currently promoting his latest autobiography, My Decade in the Premier League, which is also being serialised by the Daily Mirror. In the latest extract, Rooney admits he regreted asking for a transfer.
Rooney issued a statement in September 2010 in which he questioned United's ability to attract top players and indicated he wanted to leave.
Two days later, though, he performed a dramatic U-turn and signed a new five-year contract.
He wrote: "In September 2010 my ankle puts me on the sidelines.
"I get frustrated with myself, my game, my injury, and everything around me.
"I'm stuck in a cycle of bad form but I can't get out of it.
"And that's when I make the biggest mistake of my football career.
"In October, I release a statement which publicly questions my happiness at Old Trafford. Am I better off elsewhere?
"Everyone makes a fuss. There are discussions inside United to sort out the issue, people outside United chuck their opinions around, but the thing is, nobody really knows what's going on in my life.
"None of them understand where I am in my career. They don't know where my head's at.
"The only person who really knows what's going on in there is me, but even I'm not sure what I want."
He continued: "Then the manager has his say. 'Sometimes you look in a field and you see a cow and you think it's a better cow than the one you have in your own field. And it never really works that way'.
"He's saying the grass isn't always greener, and he's right.
"I like what's in my field. I'm wrong. United want the same as me: trophies, success, to be the best."
Meanwhile Rooney told the Manchester Evening News that his recovery is on track after suffering a gash to his leg in a tackle against Fulham a fortnight ago.
"The injury is going well. It could have been a lot worse than what it was. It is up to the doctor. When he declares me fit I will be ready.
"What I don't want to happen is to come back too early when it is not quite healed and it opens up again first game. That would just set me back again another four weeks."
"Overall, I think at the most I will miss four games."
He added that he was keen to get back onto the pitch to start building a partnership with summer signing Robin va Persie.
"I am looking forward to getting back into the team and trying to forge an understanding with him (Van Persie)," Rooney added.