Manchester United boss Sir Alex Ferguson could be without Anderson for up to a month after the Brazilian midfielder picked up a hamstring injury during his side's 4-3 victory over Reading on Saturday.
The 24-year-old limped off just before half-time, having opened the scoring for Manchester United after Ferguson's side fell behind to a Hal Robson-Kanu strike.
Anderson's leveller sparked a crazy 34 minutes at the Madejski Stadium, as the two sides traded goals in a breathless first-half to leave the score at 4-3 at half-time.
The Old Trafford medical team treated Anderson on Sunday, and diagnosed a small hamstring tear. Manchester United had feared the worst after Anderson was forced off complaining of pain in his groin and abductor.
Goal.com claims Anderson will have more tests today before beginning the recuperation process. He faces up to four weeks on the sidelines.
And Ferguson admitted he's disappointed for the Brazilian, who had begun to string together a series of fine performances. Anderson has been plauged by injury since he joined United in 2007 from Porto, but had started to find his feet this season after a short run in the team.
"He's been playing really well and scored a great goal today," Ferguson told MUTV after the game. "I'm very disappointed for him."
The Manchester United boss faces a selection dilemma for the visit of Cluj in the Champions League on Wednesday - Shinji Kagawa and Nani are both at least two weeks away from a first-team return - leaving Ferguson short of options in midfield.