Manchester United striker Wayne Rooney has admitted that he made "the biggest mistake of his career" when he handed the club a transfer request in 2010.

The 26-year-old told the Old Trafford hierarchy that he wanted to leave, but two days later he withdrew his request and signed a five-year contract with the club.

In his latest autobiography, being serialised in The Mirror, Rooney has revealed what made him make his decision.

"I get frustrated with myself, my game, my injury, and everything around me," he wrote. 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.

"The manager had his say and said '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."

Rooney has scored 182 goals in 368 appearances for Manchester United.