Alex Ferguson has ruled Manchester United defender Rio Ferdinand out for another three to four weeks with a thigh injury, while Liverpool's Daniel Agger is set to undergo surgery on his back next week.

Ferdinand suffered a slight tear in his thigh during training last week ahead of the Premier League opener against Birmingham.

Initially Ferguson felt that Ferdinand would only be sidelined for a couple of weeks. However, that estimate has now been revised.

"Rio is going to be out for three to four weeks," said Ferguson.

It means Ferdinand will miss Saturday's trip to Wigan, plus next Saturday's eagerly anticipated encounter with Arsenal.

In addition, Ferdinand now seems certain to miss the next two England games, starting with a friendly against Slovenia on September 5, then a World Cup qualifier against Croatia four days later, when victory would book the Three Lions' place in South Africa next summer.

There is some good news on the injury front for United though as Ferdinand's central defensive partner Nemanja Vidic is set to make his first start of the season at the DW stadium on Saturday as United look to bounce back from Wednesday's shock defeat at Burnley.

"Nemanja has trained with us for 10 days and he is ready for the game," said Ferguson.

"Hopefully he will be okay by tomorrow."

Agger has missed the first two Premier League games of the season, having been troubled with the injury all summer, and is now unlikely to feature for the next six weeks.

Martin Skrtel is also a doubt for the visit of Aston Villa on Monday, which means that teenager Daniel Ayala stands by having made his full debut in the 4-0 win over Stoke on Wednesday.

New Greek defender Sotirios Kyrgiakos could also figure once his €1.8m move has been completed and international clearance acquired.