Kalou is however confident that his team-mate will return for the title run-in this season.
If Essien has a lengthy spell on the sidelines, as Chelsea expect, he will return to action in mid-January.
He added: �That is a big blow [losing Essien]. Essien is the kind of player who can help you win a competition but he�s out for a few months so we have to do without him and I think he will come back stronger in the end and help us to lift the trophy.�
Essien missed the end of Chelsea�s 2009-10 double winning campaign after picking up an injury at the last Africa Cup of Nations played in Angola.