The Ghana midfielder ruptured the anterior ligament and cartilage in his right knee during a training session last week. This is the third serious knee injury of Essien's career and he will be sidelined for up to six months.
Chelsea manager Andre Villas-Boas said: "Everyone at Chelsea wishes Michael well for his recovery. His team-mates and all the staff and I look forward to helping him return to playing as soon as possible."
John Obi Mikel and Ramires will offer Villas-Boas similar central midfield alternatives, as could David Luiz who can play the holding role in front of the defence.
Meanwhile, Villas-Boas has revealed his desire for Chelsea to win with style this season - and the Blues have reportedly increased their offer for Tottenham midfielder Luka Modric to ?£27million. Chelsea had a £22million bid rejected earlier in the summer but Modric wants to leave and claims a move to Stamford Bridge would be a "dream".
The 25-year-old told Croatian newspaper Sportske Novosti: "There is no doubt that Chelsea want me - they sent a concrete offer to Tottenham. I know that the new Chelsea boss said he wants me in his team. Of course I am flattered by this interest in me - it's a club that all players dream of joining, fighting for every competition available."
Villas-Boas moved to Chelsea from Porto, who scored a remarkable 145 goals in 58 games during their title-winning campaign last year.
The 33-year-old worked at Chelsea under Jose Mourinho, whose more pragmatic style reportedly frustrated the club's owner Roman Abramovich. But Villas-Boas believes the key to success for Chelsea, who are chasing their first Champions League crown, will be to take the shackles off.
"You free them (the players) from the limitations that they might have in a different kind of system but, in the end, you make them believe in their qualities and this is the most important thing," Villas-Boas told Chelsea magazine.
"I think we are on for a great season. Coming here is not just a question of big, radical changes. You have to be clear in what you do and decide well and I'm confident that we have enough people with the quality here to go forward."
Source: PA
Source: PA