Chelsea goalkeeper Thibaut Courtois requires knee surgery and will be out for "quite a long time", according to Jose Mourinho.
The Belgium international sustained the injury in training and is now set for a lengthy spell on the sidelines.
It is another blow to Mourinho, whose side have made a slow start to the defence of their Premier League title by claiming just four points from their opening four games.
Mourinho said at Friday's press conference: "Thibaut Courtois was injured in training, he needs surgery on his right knee and he will be out for quite a long time."
Chelsea go to Everton on Saturday hoping to register their second away win of the season, and Mourinho insisted it was not all doom and gloom at Stamford Bridge.
"We are strong, together. I believe in the players, they believe in me. We are positive," he added.
"Every game is important. We are in the title race but we need points. We go with the intention to win the match."
Oscar will miss the trip to Goodison Park through injury but Mourinho confirmed the Brazil midfielder could feature in Wednesday's Champions League opener against Maccabi Tel Aviv.
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