Month on the sidelines: John Mikel Obi
Mikel damaged medial ligaments in the defeat at Arsenal on Monday when he was caught late by a nasty challenge from Robin van Persie.
Having started the first 18 Barclays Premier League games for Chelsea, the Nigerian missed Wednesday's1-0 win over Bolton and is not expected to be back for three more weeks.
It is bad news for the champions, with Frank Lampard only just back from injury, Michael Essien playing with a nagging knee problem and Ramires still adjusting to English football.
Lampard played 180 minutes in three days this week after four months out but there is little scope for rotation in Chelsea's midfield because Yossi Benayoun and Yuri Zhirkov are also out.
Ancelotti is reportedly reluctant to recall Michael Mancienne, who could play in either defence or midfield, from his season-long loan at Wolves, even though a clause in the deal allows for a January return.
The defence will be exposed against Aston Villa tomorrow, with Branislav Ivanovic suspended and Alex injured.
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