According to reports from SkySports, Manchester United midfielder Anderson will be sidelined until after Christmas with a hamstring injury.
The 24 year old Brazilian limped out of the Reading last Saturday after being substituted at half-time.
The former Porto player had been enjoying a good run of form in recent weeks.
United boss Sir Alex Ferguson said: “It is a hamstring. It will be three or four weeks. It is not serious but it is a hamstring.”