Roy Keane wishes he had not apologised to Alex Ferguson

London: Former Manchester United captain Roy Keane regrets having apologised to Alex Ferguson after the falling-out which led to him leaving the club in 2005, leaked extracts from his new autobiography have revealed.

The book, "The Second Half", is not due out until Thursday but parts of it appeared online on Monday and a Manchester supermarket mistakenly put some copies on sale before hastily withdrawing them.

Ferguson criticised Keane in a book of his own last year, and said he had "a savage tongue". The final straw in their relationship had come when Keane did an interview for the club's in-house television station MUTV, criticising a number of his team mates for a poor performance.

United declined to transmit it and Ferguson insisted on the whole squad watching a video before deciding Keane would have to leave.

There had been widespread anticipation over the volatile Irishman's response. But amid a welter of expletives, the strongest criticism Keane comes up with is that United could have told him: "Keep your head down, play a few games and come the end of the season we'll say it was best for you to go."

Instead, he writes, Ferguson and chief executive David Gill already had a statement prepared about his departure when he was summoned to the manager's office.

Soon after leaving for Celtic, where he played only a handful of games before retiring, Keane apologised to Ferguson.

"Now I kind of wish I hadn't," Keane writes. "I was apologising for what had happened -- that it had happened. But I wasn't apologising for my behaviour or stance. There's a difference -- I had nothing to apologise for."

The former Republic of Ireland international says tensions had been evident at a pre-season training camp that season, when he came close to hitting the first-team coach Carlos Queiroz, who accused him of lacking loyalty.

One person he did hit, he admits, was goalkeeper Peter Schmeichel, in a hotel fight that woke up United director Bobby Charlton and left his team mate with a black eye.

He also says he has no regrets over inflicting the injury on Manchester City's Alf Inge Haaland in 2001 that effectively ended the Norwegian's career.

After managing Sunderland and Ipswich Town with little success, Keane worked as a television pundit, which he says was too easy and did not excite him.

He is now assistant manager of the Republic of Ireland and Aston Villa.