Manchester United manager Sir Alex Ferguson has confirmed that Anderson could be sidelined for up to five weeks with a hamstring injury.
The 23-year-old midfielder has made only five appearances for the Red Devils this season through injury.
"Ando could be out for four or five weeks due to his hamstring," Ferguson told reporters. "Some hamstrings are relatively straightforward but we have to wait and see how he is in the next week or so to get a better idea of where we stand with him."
United travel to Athletic Bilbao on Thursday in the second leg of their Europa League last-16 tie.
