London - Chelsea's troubled start to their Premier League title defence suffered a fresh blow on Friday when it emerged that goalkeeper Thibaut Courtois required knee surgery.
Sources close to the player who has a torn meniscus in his right knee expect the Belgian star to be sidelined for between 10 and 12 weeks.
Courtois returned from international duty after playing in Belgium's 1-0 win over Cyprus last Sunday, only to suffer the injury on Wednesday.
Also read: Old Trafford will be bouncing - Giggs
"Everybody came back well from the national teams but Courtois was injured in a training session and I cannot tell you much but I can tell you he needs surgery in his right knee and as a consequence he will be out for quite a long time," manager Jose Mourinho said.
"I cannot be more specific about the injury and the time he will be out. "I just know he will be out for some time."
Mourinho, however, expressed full faith in 8 million ($12.4 million, 11 million euros) signing Asmir Begovic to replace him.
"It's a big blow but you will not see me speaking again about Thibaut. He's injured, he's injured.
"It's 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. Begovic is very very good. I'm sad for Thibaut and sad for the team but we have a top goalkeeper and Begovic will be in goal."
The injury only adds to Chelsea's concerns ahead of a trip to Goodison Park that is already underscored by flashpoints and controversies.
Mourinho's side have only four points from four games, the second worst start by a team defending the Premier League title, and face an Everton whose manager Roberto Martinez and owner Bill Kenwright have been so publicly critical of Chelsea's unsuccessful pursuit of 21-year-old defender John Stones.
Mourinho played all of that down, and insisted that his team's performances have been better than results have suggested.
"What Martinez says for me means nothing and I don't comment. The only thing I can tell you is that I expect Stones to play with Jagielka and we know their qualities and we are going to try to be successful.
"Every game is important and we are in the title race. Yes, we are. We need points but every game is difficult.
"Everton is not different. Every team is getting better. Every team has economic power and players to play for title contenders. Every point is more difficult to get. We know that. We have every intention to win the match but with respect."
Chelsea ended up signing Papy Djolobodji from Nantes as a cut-price alternative to Stones.
Mourinho admitted it was not his choice, but that he fully trusted the judgement of those who identified the 26-year-old, who he stressed will be a "fantastic squad player".
"It was the choice of someone I trust completely. Which is the same. I don't know every player. My job doesn't allow me to travel and spend hours watching players.
"In some moments of the market, under certain circumstances, there are moments when you have to trust or not the people you work with. In my case, I trust because the same person who told me Djilbodji can be a good squad player was the same person who told me (Kurt) Zouma can be a fantastic player for us. "
Club owner Roman Abramovich was also seen at the Cobham training ground, but Mourinho was reluctant to reveal what they were to discuss.
"I don't have to tell you."