The Irish midfielder revealed his plans in a live phone-in on United's television channel, MUTV, telling one fan of his "gut feeling that it would be best to make a clean break" from the club he has served with such distinction for 12 years.

Keane, who turns 35 in the summer, insisted that he would not move to another Premiership club, and made it clear he would like to realise a long-cherished dream of playing for Celtic, the team he grew up supporting.

"I'd like to play on for another year or two but I don't think it will be at United," Keane said.

"It would be a good experience for me to play for another team, another country, another dressing room. If I'm going to become a manager it would be good for me to experience a different environment."

Just in case Celtic manager Gordon Strachan did not get the message, Keane added: "When I say I might play for another team I don't necessarily mean an English team. I think that would be hard for me to stomach. I wouldn't fancy coming back to Old Trafford and going into the away dressing room."

Strachan refused to comment on whether he would be interested in taking Keane to Parkhead. "Since I've been at the club, or any other club I have been at, I've never spoke about anybody else at any other club," he said. "I'm not going to change it now. If I say anything at all there will be headlines all over the place and I want to concentrate on Livingston tomorrow.

"It's not fair on the player or the club. It's as simple as that."

Keane's comments will inevitably dismay United supporters who are already disgruntled by the extent to which the club has slipped behind Chelsea, on and off the field.

It was not clear on Friday whether United manager Sir Alex Ferguson or any of the Old Trafford hierarchy were aware of Keane's intentions, but Ferguson's assistant Carlos Queiroz recognised that the Irishman would be a hard act to follow.

"You don't replace great players like Pele, Maradona, Eusebio or Roy Keane," the Portuguese coach said. "You just create new players in new teams. That is why the game moves forward."