After their shock shock 1-0 defeat away to Premier League newcomers Burnley on Wednesday United had some good news Friday with another defender, Nemanja Vidic, now fit and set to line up for the match against Wigan on Saturday.
However that has been offset by the loss of Ferdinand. He suffered a minor muscle tear in his thigh last week and was set to be sidelined for two weeks. But it has emerged that he needs more time to recover.
"Rio is going to be out for three to four weeks," said Ferguson.
Ferguson added: "We don't have any new injuries from Wednesday night. They're all fit," he said.
"The one position we're hoping for an improvement in is with Vidic. He's trained now for ten days and he is ready for a game. Hopefully he'll be OK for Saturday.
"Gary Neville played 15 minutes at Burnley and he could be ready too, and that gives us experience at an important time after defeat on Wednesday."
As well as missing key matches for United Ferdinand now seems certain to miss the next two England games, a friendly against Slovenia on September 5, then a World Cup qualifier against Croatia four days later where victory would book England's place in South Africa next summer.