"My body is not happy any more," he said.
"I always promised I'd move on when this moment arrived. It's time to end my playing career.
"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.
"It has taken a month of soul-searching to make this decision, the most difficult of my life.
"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 my life. It's over."