Salomon Kalou and Yossi Benayoun are facing a few weeks on the sidelines after picking up injuries in Chelsea's Carling Cup defeat by Newcastle United.
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.
Both players seem certain to miss Saturday's trip to Manchester City where Chelsea will be looking to maintain their 100 per cent start in the Premier League.
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 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."
Kalou has enjoyed an impressive start to the new campaign after scoring four Premier League goals, while Benayoun has largely been used as a substitute since his move from Liverpool.