The Brazilian midfielder has received another setback after featuring in the Red Devils' squad just 16 times this season thanks to a spate of injuriesManchester United manager Sir Alex Ferguson has confirmed that midfielder Anderson is set for another spell on the sidelines.
The Brazilian, who signed from Porto in 2007, has struggled with injuries this term, making just 16 appearances.
Now, after looking set to make a return to first-team duty upon earning a place in the squad against Athletic Bilbao, he has received another setback in training.
"Anderson could be out for four or five weeks due to his hamstring," Ferguson told the club's official website.
"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 [in terms of recovery]."
The Scot also looked forward to the Red Devils' Europe League second-leg tie against the Spanish outfit on Thursday, as they attempt to overturn a 3-2 deficit in Bilbao.
"It's a difficult tie for us," he added. "Bilbao have a tremendous advantage after winning at Old Trafford. It's a challenge but not one that is beyond us.
"Our record away from home helps us - we've done very well. We're going to need a good performance."