Chelsea's Thibaut Courtois out for approximately three months and needs knee surgery

Chelsea goalkeeper Thibaut Courtois will be out for approximately three months, according to Sky sources, after manager Jose Mourinho confirmed he needs knee surgery.

Courtois suffered the injury during a training session at Cobham this week and Mourinho admits he is unsure how long the goalkeeper will be unavailable for.

"Courtois was injured in a training session with the goalkeepers and I cannot tell you much, but I can tell you that he needs surgery in his right knee," Mourinho said.

"As a consequence of that he will be out for quite a long time. I cannot be at this moment more specific about the injury or the time he will be out."

Asked if he could give a rough idea how long the Belgium international would be sidelined, Mourinho replied: "No, I don't want to go in that direction. I just know that he will be out for some time.

"I will wait for [Chelsea medical director] Doctor Biosca to be more specific after surgery and I think today [Friday] we will be ready to give some more information.

"It's a big blow but you will not see me next week speaking again about Thibaut. If he is injured, he is injured.

"It is not easy to have the best goalkeeper in the world injured but it's easy to have one of the best goalkeepers in the world to play. We have [Asmir] Begovic to play and he is very, very good.

"I am very sad for Thibaut. I am very sad for the team obviously but we have a top goalkeeper and Begovic will be in goal."  

I am very sad for Thibaut. I am very sad for the team obviously but we have a top goalkeeper and Begovic will be in goal.

Mourinho has also confirmed Oscar will miss the weekend visit to Everton but says the midfielder could return for Chelsea's Champions League game with Maccabi Tel Aviv on Wednesday.

The 24-year-old was forced to withdraw from the Brazil squad that played two friendlies in the United States during the international break and has not recovered in time for the trip to Goodison Park. 

Chelsea have taken just four points from their opening four games and are eight points behind leaders Manchester City.

And Mourinho emphasised the importance of Saturday's trip to Merseyside, insisting his side will aim to take three points against Roberto Martinez's side.

"Every game is important," he said. "We are in the title race but we need points. We go with the intention to win the match.

"We are strong, together. I believe in the players, they believe in me. We are positive."