Premier League - Chelsea hit by double injury blow
The pair were injured as a last-minute goal from Shola Ameobi earned Newcastle a place in the fourth round after a 4-3 win in West London.
But the loss of two key players and talented youngster Gael Kakuta were uppermost in the mind of the Italian coach ahead of Saturday's Premier League clash with Manchester City at Eastlands.
Ancelotti confirmed Benayoun, who went off after all three substitutions had been made, and Kalou would miss the game against Manchester City.
"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 Ancelotti.
"We will know more (on Thursday) 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."