Ivory Coast forward Kalou hurt his thigh just 10 minutes after coming on as a half-time substitute against the Magpies, while Benayoun's departure with a calf problem left Chelsea with just 10 men.
Gael Kakuta also suffered an injury in the 4-3 home loss to Newcastle and Ancelotti is awaiting confirmation of the extent of the problems.
"Kakuta had a problem on his leg after the tackle in first half while Benayoun's injury is his calf and Kalou hurt his thigh," said Carlo Ancelotti.
"We will know more tomorrow, but they don't look good. They will miss the next few games.
"These things can happen in football. It was a strong tackle on Kakuta and he was unlucky. The problem with his back is from the fall."