The shock decision, which leaves Ireland's hopes in tatters, follows Keane's strong criticism of the team's training facilities and his threat earlier this week to go home before the tournament which starts on May 31.

A FIFA spokesman said a player could only be replaced in a squad because of a serious injury. "This appears not to be the case with Roy Keane," he told Sky Sports television.

Ireland, which handed in its official 23-strong squad on Wednesday, may therefore start the tournament with only 22 men.

Ireland coach Mick McCarthy is expected to hold a news conference later.

Earlier on Thursday the Manchester United midfielder, who played in the 1994 World Cup, announced he would quit international soccer after the 2002 tournament. "Yeah, that will be it. That will be it for me and life goes on," Keane said.

Keane's threat to fly home from the training camp was for "personal reasons" but he changed his mind after talking to Manchester United manager Alex Ferguson.

"It was the tip of the iceberg," Keane told Irish reporters in Saipan where the team is preparing for its opening match against Cameroon. "I've basically had enough of certain things."

Keane, who has played almost 60 games for Ireland, was irate about the state of the pitch in Saipan which he said was as hard as a car park. "He's a good man and he gave me good words of advice," the United player said of Ferguson.

"You have to listen to these people. The manager has the same temperament as me, he understood what I was going through. He told me to stick it out, but this is it.

"You've seen the training pitch and I'm not being a prima donna. Training pitch, travel arrangements, getting through the airport when we were leaving, it's the combination of things.

"I can't imagine any other country, countries in the world who are far worse off than us, playing on something like that," the 30-year-old said.

"But you know, we're the Irish team, it's a laugh and a joke. We shouldn't expect too much."