In a column in The Sunday Times, he writes: "You're supposed to wake up every morning and look forward to the challenges of the day but now my body is not happy any more.
"I'd always promised I'd move on when this moment arrived. It's time to end my playing career.
"It has taken a month of soul-searching to make this decision, the most difficult of my life. Playing football has been that life for 20 years, and it’s hard to accept that at 4.50pm at Maine Road on May 11 the final whistle will sound on more than just another game and another season. There’s a time to let go, to get on with life. It’s over.
"My retirement has come in phases. I left Manchester United in 1999 so that I could play somewhere less hectic and have more time to recover between games. In spring 2001, I gave up international football and planned to quit completely when my season finished with Sporting Lisbon. An old boys’ match in Denmark changed everything — there was no spark in the game, it was just a social occasion, and I realised I wasn’t ready to give up the thrill of competition. So I came back to England, and enjoyed these past two years with Aston Villa and Manchester City. This time I’m ready. I’m even ready to try playing just for fun.
"I’ve been particularly happy about how fans in Manchester — both red and blue — have accepted me in a City shirt. The nice thing was that Kevin didn’t agree with me. He said: "You’ve been good for the team. I want you to play another year." I’d be 40 at the end of that season, so it was a great compliment. It confirmed I’m going out at the top, and I always wanted that."
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