Knee surgery will delay Foster's United return

The 24-year-old had been suffering knee problems during the latter half of last season, which he spent on loan at Watford.

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Injury setback: Ben Foster

And he pulled out of the England B international with Albania at the back end of last month to undergo tests.

Now Foster's worst fears have been realised, with United releasing more specific details of an injury which will keep sidelined for months.

"Ben Foster has a cruciate ligament injury in his right knee and will require an operation in two to three weeks' time," a United spokesperson told www.manutd.com.

In a statement, the club added: "The injury was then jointly assessed by United and England's medical staff after the goalkeeper reported for international duty at the end of May.

"While the Reds' medical staff have not put a timescale on the 24-year-old's return to action, he is likely to spend a lengthy spell on the sidelines."

It is almost certain to be the early months of 2008 before Foster is in action again.

The injury is a bitter blow to Foster, who has been outstanding in two seasons at Watford and had already spoken optimistically about his chances of succeeding Van der Sar as Sir Alex Ferguson's number one for the Premiership champions next term.

If Foster had succeeded in that aim, he could easily have been vying with Paul Robinson for the England slot as well.

Instead, the former Stoke man now faces months of rehabilitation.

While he will be bolstered by the knowledge plenty of United players, including Roy Keane, Ruud van Nistelrooy and Wes Brown, have battled back from similar injuries, it is still a gloomy way to end the campaign.

The news also means Tomasz Kuszczak, who spent last term as Van der Sar's understudy, is now virtually certain to remain at Old Trafford rather than go out on loan as some pundits had predicted.

Meanwhile, Sir Alex Ferguson believes Cristiano Ronaldo has emerged as an even better player as a result of the fury he faced for his role in Wayne Rooney's sending off at the World Cup.

Ronaldo was labelled public enemy No1 over his involvement in his United team-mate seeing red during last year's quarter-final in Germany.

But the Portugal winger responded by sweeping the board at end-of-season award ceremonies.

United manager Ferguson said: "I think good people respond to adversity very well - take Eric Cantona for instance, when he came back we won the Double.

"When young Ronaldo comes back we win the league and he is the star of the season.

"They were burning effigies of David [Beckham] and what I said to Cristiano and Eric was exactly what I said to David at the time, 'They're going to boo you but that's all'."