MANCHESTER (Reuters) -- Manchester United captain Nemanja Vidic faces longer on the sidelines than initially expected with manager Alex Ferguson saying on Friday the defender would be out for up to five weeks with a calf injury.

There was better news for fellow centre back Rio Ferdinand, who had been ruled out for six weeks with a hamstring injury but who could now return in time for the Premier League champions' home match against Arsenal on Aug. 28.

Ferdinand and Vidic picked up the injuries in last Sunday's season-opening 2-1 victory at West Bromwich Albion.

"Vidic has a calf muscle injury which means he will be four to five weeks. It is difficult to say with calves but it is longer than we thought," Ferguson told reporters, referring to original expectations the Serb would be out for two weeks.

"Rio is not as bad as we thought so he could be ready for our game against Arsenal. I don't think he'll be ready for Monday but it is amazing how it can change in a few days."

Tottenham Hotspur visit Old Trafford on Monday.

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