The Reds striker was absent from the Boxing Day squad to face Newcastle United and is expected to sit out the next few matches as well, according to his manager.
"Wayne did it towards the end of training yesterday," Sir Alex Ferguson revealed on MUTV. "He was trying a volley when he strained a ligament behind the knee. He could be out for two to three weeks. It's unfortunate because I thought after his performance on Sunday [at Swansea], he would have been brilliant today. You don't get two performances from Wayne like the one he gave on Sunday. He was desperate to play but unfortunately we couldn't risk him."
As for the other men missing the Magpies clash, Sir Alex explained: "Danny Welbeck took ill in the team hotel last night and Ashley Young got injured in training also. Phil Jones got his injury at Swansea and we couldn't risk Vida [Nemanja Vidic] after his first full game back. He had a little bit of soreness in his knee which is to be expected after being out so long. We've got other players out too so all in all, given the problems I had with team selection, the players were magnificent today."
A further update is likely when the boss holds his pre-match press conference on Friday.