Michael Essien has revealed that he remains uncertain when he can return from the knee injury that is also threatening to rule him out of the World Cup.

The Ghana international has not played for Chelsea since December and only made a couple of appearances for his country at the Africa Cup of Nations in January before being ruled out indefinitely.

Essien revealed that he had suffered a couple of setbacks in recent weeks and he is now unsure when he will be able to return to action.

"I was hoping to be available for the home game against Inter, but the healing has taken a bit longer because my knee kept swelling," Essien told his official blog.

"In two weeks I ended up having four lots of surgery to try to get the fluid away from the area. Finally it seems to be OK and I am making progress. I know I just have to be patient and give it time to settle down and heal."

Essien has watched Chelsea crash out of the Champions League and lose ground in the Premier League title race, but he remains calm about his future.

He added: "On a positive note I am feeling mentally strong and I try to stay philosophical about injuries.

"There are worse injuries than mine and there are people suffering with far more serious problems than this."