Newcastle have confirmed that the procedure had been carried out and that the player would remain in America for another week before beginning the long haul back to fitness.

Shearer had initially undergone surgery on the knee in which he has been suffering from tendonitis for almost a year in December, but it became clear in recent weeks that another operation would be needed in a bid to solve the problem once and for all.

"Alan Shearer successfully underwent surgery yesterday," a club spokesman said. "He should remain in the States for approximately one more week before returning home for rehabilitation."

United boss Bobby Robson admitted last week that the process of returning to full fitness could take up to four months, but he is now putting no figure on the rehabilitation period.

"Bobby says the rehabilitation will take as long as it takes," added the spokesman.

Shearer has been a shadow of his former self throughout an injury-plagued season after trying to battle through since last summer.

He initially had a steroid injection in the injured knee during England's Euro 2000 campaign, and then had two more - the maximum allowed - before it became clear that there was no alternative to surgery.

He had the initial operation after the 2-0 defeat at Derby on December 23, and just as he promised, was back in harness weeks ahead of schedule two months later for the 1-0 defeat by Manchester City at St James' Park on February 24.

But the following game - a 1-1 draw at Everton on March 3 - proved to be his last of the season, and although he hoped a second bout of surgery would not be required, he knew the writing was on the wall as he jetted out to Colorado on Sunday.

However, both Shearer and his manager have insisted all along that the problem is not career-threatening and that the latest move is a relatively minor one to clean up the area around the initial injury.

Both men will be hoping that diagnosis proves to be right after a disappointing season during which the £15m striker has been able to contribute just 23 games and seven goals, the last of them a double in the 2-1 win over Ipswich on November 4.

"We haven't really seen the real Alan Shearer all season because of this injury," admitted Robson. "He's battled on, but we have to get him right for next season."