"He is getting better but he needs to have some weeks again, maybe two weeks to be fit 100%," said Ancelotti.
"He had a problem on his adductor and we have to pay attention."
Defender Alex and strikers Kalou and Sturridge could be back in action next week according to the Blues boss.
Alex injured his thigh during Chelsea's 2-0 win over Arsenal on 3 October, while Kalou damaged his calf in the Carling Cup defeat against Newcastle on 22 September and Sturridge has picked up an ankle injury.
Ancelotti also said he was shocked when Benayoun's torn Achilles tendon was discovered while the midfielder was on international duty with Israel earlier in October.
The injury puts Benayoun out of action for six months.
"We are sure that when he left England that he didn't have a tear on his tendon, we are sure of this," stated Ancelotti.
"He had a problem on his calf, and the MRI showed this, but the tendon was clear."
Chelsea are four points clear of Manchester City at the top of the Premier League and head their Champions League group on goal difference from Spartak Moscow, having won both matches so far.
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