Rio rocked as he heads for a scan

Ferdinand reported to United's Carrington complex on Monday but went for a scan instead of training.

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Ferdinand at full stretch: United's defender celebrates a goal against Aston Villa but he's a doubt for the Arsenal clash

The England centre half fears a recurrence of a groin problem that forced him to miss four of United's final six games in the run-in to regaining the title last season.

Coming on the day when it was also revealed midfielder Paul Scholes will be ruled out until February, it was hardly the news manager Sir Alex Ferguson needed before the clash with rival Arsene Wenger and his Premier League leaders.

Ferdinand was replaced by Gerard Pique 20 minutes from the end of Saturday's convincing 4-1 win over Middlesbrough, a victory that lifted United to the top until Arsenal took a point from Liverpool on Sunday.

Ferdinand's solid defensive partnership with Nemanja Vidic had been a key feature of United's return to form along with the blossoming partnership in attack of Wayne Rooney and Carlos Tevez. Ferguson's recordequalling side have now hit four goals past their last four opponents.

United insiders expect Ferdinand to bite the bullet for Saturday's crucial lunchtime showdown at the Emirates, which is likely to be one of a handful of matches this season that settle the destination of the title.

But there is concern that Ferdinand's injury will have to be addressed in the long term if it keeps returning to bother the defender, who is 29 next month.

Scholes will not kick another ball in anger for at least another 12 weeks and will have surgery on a knee on Thursday after his specialist confirmed he was suffering from ligament damage. There had been fears that the talented midfielder might be suffering from a cruciate injury after an initial scan proved inconclusive on Friday.

The 32-year-old former England player, who beat a career threatening eye injury last season, was hurt in training a week ago in Kiev while preparing for a Champions League tie.

Scholes must now sit out the next three months as United surge on towards what Cristiano Ronaldo believes will be their 'heavyweight championship'.

Old Trafford's darling has promised to keep frustrating the defenders who leave him black and blue, and warned: 'With Carlos Tevez, Nani and Anderson, we are more heavyweight this season.

'Now, when teams come to shut up shop, we have more ways of unlocking them. It's exciting. We're certainly better than last year. And if defenders want to put the boot in, I'll keep taking it. I'm used to it now.'

Ronaldo added: 'I was delighted that Real Madrid were so interested in signing me, but United have become everything to me. I'm going to be here for many years and I'm going to be very happy.'

Sunderland manager Roy Keane is ready to raid his former club in January with a £2.5million offer for 20-year-old United central defender Jonny Evans, who impressed during a successful loan spell at the North East club last season.

Keane could not persuade his former boss Ferguson to sell the Northern Ireland international this summer but Evans has failed to break into the Premier League ranks at Old Trafford.

Keane, however, will be able to assure the ambitious youngster that he will have a regular starting place if he joins him at the Stadium of Light.

United goalkeeper Edwin van der Sar, who made his debut for Holland in June 1995, has revealed that he intends to retire from the international stage after next year's European Championship.

Van der Sar, 37, previously at Ajax, Juventus and Fulham, has made a record 121 appearances for his country. He said: 'I will stop with Oranje after Euro 2008. The time has come.'

Fellow Dutchman Jaap Stam, who won three League titles and the Treble with United in 1999 and is still celebrated in song at Old Trafford, has retired from football at 35 because of a lack of motivation.

Stam, who retired from international football three years ago after winning 67 caps, said: 'I no longer feel 100 per cent.'

The Ajax centre half was sold to Lazio in 2001 after falling out with manager Ferguson — who he claimed in his outspoken book had ' tapped him up' before United signed him from PSV Eindhoven in 1998.