ROY Keane has revealed he joined Celtic out of defiance towards Gordon Strachan - and then contemplated quitting the club after one training session.

Speaking yesterday in Dublin at the launch of his autobiography, The Second Half, the Irishman spoke candidly about his six-month spell at Celtic Park from December, 2005 until May, 2006.

Keane was leaving Manchester United after a fall-out with Sir Alex Ferguson and had offers from Real Madrid, Everton and Bolton. But the lure of proving Strachan wrong and playing in an Old Firm game convinced Keane to move to Scotland.

With typical, brutal honesty, Keane said: "Real Madrid offered me a year and a half. Emilio Butragueno made the call and said: 'Roy, we'll be glad to have you.' I met David Moyes at his house and was impressed with what he wanted for Everton. When a club is interested, the manager generally sells it to you. But I met Gordon Strachan in London at Dermot Desmond's house. Gordon told me: 'I'm not really worried if you sign for us or not. We're okay without you.' So I said to myself: 'F*** him, I'm signing.'

"I think it was one of the reasons I signed for Celtic - to prove Gordon wrong. He was letting me know he wasn't desperate for me; he was being a bit coy. But there was a bit of defiance from me.

"My hip had been causing concern and after my first training session I drove back to my hotel in Edinburgh and lay on the bed. And my hip - I've never known pain like it. My hip was f****** screaming. Just from the warm-up and the training. I lay there thinking - I don't want to go back. But I need to - I have to. You should have retired. You should have just packed it in. But I couldn't leave after my first day. Imagine how that would have looked."

Keane won an SPL championship and the League Cup with Celtic and then retired from football at the end of that season.

His favourite moment in Scotland was defeating Rangers 1-0 in a league game at Ibrox. He recalled: "I look back at my time there and I'm a bit embarrassed. I only played 12 or 13 games.

"I enjoyed the Old Firm game. We won 1-0. Maciej Zurawski scored the goal. I was man-of-the-match. I got a yellow card for a foul on Dado Prso and they were baying for a red card.

"The atmosphere was brilliant, f****** electric. The hatred - I enjoyed all that. The dressing-room afterwards was great. I met great people at Celtic - from John Clark to the late Tommy Burns. I've no regrets about signing. It's a brilliant club.

"When I phoned Gordon at the end of the season to tell him I was going to have to call it a day because of my hip, Gordon went: 'All right, it's for the best.' And I was saying to myself, 'Try and persuade me, for f***'s sake. At least pretend.'

The Second Half, by Roy Keane, is published by Weidenfeld and Nicolson and on sale at £20.