But, as with so many other critical points in his career, Keane is determined the critics will be proved wrong.

“People are saying I’m not the player I was and I’m finished with football,” said Keane.

“I’ve been a professional for 13 years and had a lot of pats on the back but this is the worst criticism I have had in my career.

“You have to try not to get too carried away with the success and try not to get too down with all the negative stuff.

“I have not played as well as I can but I am not playing as badly as some are suggesting. I am more than confident I will be as good as ever and playing at the top level for another three years.

“Please God, I have three years left at Manchester United but if not I still think I will be playing at the top level somewhere.”

Like his shadow, controversy is never far from Keane.

The tough-tackling and equally tough-talking Irishman has become as infamous for what he says off the pitch as what he does on it.

His rants have become part of football folklore – from his prawn sandwich blast right up to his outburst at Mick McCarthy and the Republic of Ireland’s preparations which cost him his place at the 2002 World Cup finals.

United manager Alex Ferguson, though, would not have Keane any other way and he values the midfielder’s forthright views.

Ferguson sees his captain as his enforcer in the dressing room.

Keane’s drive and determination alone have won more games than United supporters would care to count, have turned around seemingly lost causes into dramatic victories.

If United’s standards slip then Ferguson knows he can rely on Keane to tell his team-mates to pull up their socks, euphemistically speaking.

In his autobiography he famously claimed too many of his United team-mates were consumed by their passion for “Rolexes, cars and mansions” when they should have been be concentrating on winning trophies.

Keane insists he does not say things just for effect. He claims he merely tells it as he sees it and if that upsets anyone, then tough.

“I just think that’s the way I am,” he said. “There’re enough people who sit on the fence and I’m not really one for doing that.

“Life’s too short and I know sometimes you need to be a bit diplomatic, but sometimes you need to say what’s what and what’s not.”

Ferguson believes that Keane will be an “absolutely brilliant” manager if he moves into the dug-out when he hangs up his boots.

Keane has admitted he would like to move into management when he retires as a player and Ferguson insists the Irishman has the potential to make the transition.

“Absolutely no doubt about that. If he wants to do it he’ll be an absolutely brilliant manager,” said Ferguson.

Keane has revealed he has taken the first tentative steps towards becoming a coach – even though he stresses he wants to play on for three more years.

Keane says he has spoken to Steve McClaren – now Middlesbrough’s manager after a spell as assistant at Old Trafford – about the coaching road he needs to take.

“Being 32 in August you start to think of these things,” said Keane. “If you had asked me two years ago about management, I would have told you it wasn’t even on my mind.

“Now as I have got a bit older, I have spoken to Steve McClaren and one or two other people and started to think along those lines about getting my coaching badges and being a manager some day.

“It is a road I think I would like to go down but again it is dangerous thinking too far ahead.

“Like most things in football, once you start planning things ahead they go out of the window. But being a manager does appeal to me.”

But the thirst for action still burns within Keane.

“I am doing everything to make sure I can carry on as long as I can at United,” he said. “Not a day goes by when I am not looking to do something that could prolong my career.

“I am looking at everything, whether it is stretching, footwear, diets, weights, making sure I get enough rest.

“When you hit 30 that’s when you start thinking, ‘I want to hang in there, as long as I can’.

“I don’t want to be hanging in there and just getting by. I want to still be at the top. That’s why I am constantly looking around, like you do in life, as to what will make me better and help me.”

Keane says being laid up after the hip operation gave him a different perspective.

“Every time you come back from a setback like that you do appreciate the game that much more,” he told the Manchester United Magazine.

“Maybe it shouldn’t take a setback or an injury to make you enjoy it. Even though you do enjoy it when you are fit, maybe it is not to the extent that you realise how lucky you are, not just in football but in life too.

“When I was out injured it reminded me of how much I enjoyed the game and I couldn’t wait to get back.

“Nobody wants to be injured but the benefit is when you come back you are fresh because you have been out of the team and you can learn a lot while you are out watching.

“Every game I am feeling better and stronger. But like any footballer there is always plenty of room for improvement. That’s the way I have thought throughout my career.”

Keane accepts he now plays a holding role in midfield, rather than racing box to box.

“I think that is what the future will have to be for me – a more withdrawn role,” he said. “It doesn’t mean I can’t get forward.

“Hopefully that will take nothing away from what I contribute to the team. If anything I think it will help.”