Virgil van Dijk has undergone "successful" knee surgery to repair the anterior cruciate ligament damage he sustained in the Merseyside derby, Liverpool have confirmed.
The Dutch centre-back suffered the injury in a challenge with Everton goalkeeper Jordan Pickford during the 2-2 draw at Goodison Park on October 17.
"The Liverpool defender's planned operation took place in London and was conducted successfully," read a club statement.
"Van Dijk will now immediately focus on the beginning of his rehabilitation with the support of the Reds' medical department.
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"No timeframe has been placed on the Dutchman's return to action."
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Liverpool manager Jurgen Klopp is pleased the operation was a success but has warned Van Dijk has a long road to recovery.
"Surgery was successful, which is really good news - the best news you could get," said Klopp ahead of Saturday's Premier League match against West Ham, live on Sky Sports.
"This time is always unpleasant. Everybody who has had surgery knows that. You don't wake up and everything is fine, you feel the surgery.
"But he is good, as good as he can be."
When asked if he expected Van Dijk to make a strong recovery, Klopp added: "100 per cent. Clear to say, he is a quick healer and a pain coper. All these things, yes they help."
In Van Dijk's absence, midfielder Fabinho had started at centre-back against Ajax, Sheffield United and FC Midtjylland.
But the Brazilian suffered a hamstring injury against FC Midtjylland in the Champions League on Tuesday and will miss the game against West Ham.
Brazilian goalkeeper Alisson has become the latest Liverpool player to criticise Pickford for the challenge which left Van Dijk requiring surgery.
"Every goalkeeper has a different way to play and a different way to move," Alisson told Sky Sports News.
"In that moment, 100 per cent it wasn't a necessary movement. Thinking in my mind when I go to a situation I go to finish it because if I go too soft the opponent can score.
"But everyone has their own way. I don't agree with that way, everyone can see that. It was an unnecessary moment and movement."
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