Manchester United boss Sir Alex Ferguson admits his defensive injuries are becoming a major concern.

For the 4-0 win at West Ham, Gary Neville pulled up with a damaged groin in the first half.

Then Wes Brown went off late in the second to leave United with a back four comprising Ryan Giggs at left back, midfielder Darren Fletcher at right back and another midfielder in Michael Carrick partnering the diminutive Patrice Evra, who moved from left back, in the centre of defence.

It left Ferguson wondering how he was going to field a back four for the trip to Wolfsburg in the Champions League on Wednesday.

Ferguson said: "Evra must be the smallest centre half in the world. but he's a good reader of the game. He's quick and determined.

"I don't know where I'm going to get a back four for Wednesday. Probably Nemanja Vidic will be back from flu and I'll probably play Carrick alongside him."

It is tribute to the tenacity of the champions that they were able to overcome an injury list of such debilitating proportions.

The casualty list now includes Rio Ferdinand, Jonny Evans, Vidic, Neville, Edwin van der Sar, Brown and long-term casualty Owen Hargreaves.

Ferguson added: "The injuries in defence are becoming a bit of a headache to us. Carrick stepped in and did very, very well. He's got the composure and the pace and it was a good performance in the second half. We used out experience."