Ferguson has attempted to ensured Ferdinand's absence causes minimal disruption to United's season.

Apart from Monday's game against Everton, Ferdinand is likely to sit out the trip to Fulham on October 19, possibly the visit of Aston Villa the following weekend and, at the very worst, a home game against Southampton on November 2.

United's summer signing from Leeds is also now likely to be excused the draining Champions League visits to Olympiakos and Maccabi Haifa, which have taken on reduced importance given United's perfect start to the competition.

For the first time this season, Ferguson has a choice to make over who to bring in to replace Ferdinand.

Gary Neville's return from his broken foot is one alternative, with brother Phil being asked to slot in at right-back, while the more likely option is another outing for the impressive John O'Shea as Laurent Blanc's partner.

Ferguson insists there was no way of putting off the surgery, saying: "The lad's welfare is the prime concern.

"The knee has been bothering him for some time so it was decided to have it cleaned up so that he will be available for as much of the season as possible."

O'Shea has been a regular starter for United this season after developing his physique during the summer to the delight of his manager.

"Last year he was a big beanpole, but he has grown and developed his strength," said Ferguson. "He looks like a centre-half."

Long term, the 21-year-old Waterford-born O'Shea is seen as the favourite to partner Ferdinand at the heart of United's defence, although Wes Brown could pose a significant threat to that pairing should he ever enjoy a decent injury-free run.

Brown is two weeks away from a return to training after breaking an ankle against Zalaegerszeg in August, while Roy Keane is hoping for a comeback at roughly the same time following hip surgery.

With Ruud van Nistelrooy struggling to overcome a tight hamstring, United's squad depth continues to be tested, although with Neville, Paul Scholes and Quinton Fortune available again after their own problems, Ferguson is not too concerned.

"The strength of our player pool has always been very important to us," said the United boss.

"Because of injuries, we have come through a period of seven games in 20 days by virtually relying on the same bunch of lads.

"They have done fantastically well but there is going to be a time when you need to freshen up and we don't want to go to the days when we were bringing young lads in for big games and asking them to play in different positions."