Manchester United midfielder Anderson has been ruled out for at least three weeks after suffering a hamstring injury in last weekend's win over Reading.
Anderson scored United's first goal in their 4-3 victory at the Madejski Stadium, but the Brazilian was then forced off at halftime and missed Wednesday's Champions League defeat against CFR Cluj.
United manager Alex Ferguson confirmed on Friday that the former Porto star won't be back in action before Christmas, ruling him out of the Premier League leaders' derby clash at Manchester City on Sunday and the following matches against Sunderland, Swansea and Newcastle.
"It is a hamstring," Ferguson told MUTV. "It will be three or four weeks. It is not serious but it is a hamstring."