Four years after he parted company with the Ireland squad in Saipan, and nine months after his Manchester United career ended in similarly controversial circumstances, Roy Keane has conceded he would do it all a little differently if he had the chance.

"I think I have, no doubt about it, over the years crossed that white line," he told a press conference called to unveil him as the new manager of Sunderland football club at the Stadium of Light. "It has probably cost me lots - probably cost me the World Cup in 2002, you could say my United career."

Of his departure from the club he played with for 12 years, he went on to observe, "Maybe I did cross that line towards the end and was rightly punished for it, you could say."

But he pulled back on events prior to the 2002 World Cup when it was suggested that he was, in this instance too, admitting at least a portion of the blame for what happened.

"What I said I meant more in relation to United, really," he said. "When it comes to what happened at the World Cup, I would do the same again tomorrow."

The hard line was softened again, though, and he admitted that, four years on, things might have ended differently if he faced into the same situation.

"If it happened today would I do something differently?" he asked rhetorically. "I probably would, but as you get older and wiser you probably do handle different situations . . . It's just life, isn't it, I suppose."

While Keane clearly signalled that he does not feel he owes Mick McCarthy an apology, he said he had given one to Alex Ferguson and Niall Quinn for his part in the events that led to their rifts with the Corkman.

Relations, he insisted, have been warm with both since, and he appeared confident he and his former international team-mate will be able to work well together at the Stadium of Light.

"I have fallen out with literally thousands of people," he said without cracking a smile, despite laughter all around him. "I am humble enough to apologise if I have done something wrong. That's the type of character I am. I will be working with Niall and there won't be a problem."

Asked about the conversation subsequently, he suggested that Quinn had then apologised to him too, adding, "It's amazing how many things come out when you say you're sorry to someone."

Keane said the initial contact regarding the job offer had come during the summer, and it was at that point he had resolved his differences with Quinn. He had nevertheless declined the post on the basis that he was determined to obtain his Uefa A coaching badge. Even after he had done that, however, the job was still vacant, and last Monday he received another call from Quinn to sound him out.

"My attitude was that I was going to wait a bit longer, and then after the phone call, within 10 seconds, I thought, 'What am I waiting for?' The challenge is there. Sunderland is a big club, a beautiful stadium and a good fan-base . . . I thought, 'Why not? why not?'"

Despite having approached Martin O'Neill and Sam Allardyce, Quinn insisted Keane had always been "at the very top" of the club's list of targets.

"We always had our eye on what Roy was going to do after that coaching course," he continued. "We were in constant touch with Michael Kennedy, and last Monday he said the time was right to make the phone call."

The Dubliner insisted that with their man on board he and his financial backers would provide everything within their powers to ensure Keane would be able to succeed in his first management job.

"We will, hopefully, have everything Roy needs," he said. "We appreciate that Roy's not going to buy players for the sake of it, but the resources are there, and when we can get quality in and replace players with much better players we will back him."

To that end, Keane said he would use contacts established over his years in the game to recruit new players for Sunderland, but insisted he would not be rushed into things.

"I've been on the phone yesterday and this morning, which isn't like me. We have a good squad here already and my mindset is that I won't be getting anybody - because I don't want to upset myself or the players - come Thursday, or to give the fans false promises. But there are things in the pipeline."

With yesterday's media obligations out of the way, Keane will set about the task of finalising his coaching staff and preparing his team for the league game at Derby County on Saturday week.

One hundred per cent commitment from all concerned would be enough to satisfy him, he said, but whatever happens, he insisted, there'll be no "storming out" in the event that things go wrong. "It'll be my responsibility now to make sure they don't go wrong. That's the difference being a player and a manager."