Virgil van Dijk will be out of action for over a month after sustaining a hamstring injury in Liverpool's defeat to Brentford earlier this week, Jurgen Klopp has confirmed.
Defender Van Dijk was one of three players substituted at half-time in Liverpool's damaging 3-1 loss at the Brentford Community Stadium, which saw them lose ground in the race for a top-four Premier League finish.
Klopp described Van Dijk's withdrawal as precautionary after the game, but reports later in the week suggested the Netherlands captain's injury was worse than initially feared.
Speaking ahead of Saturday's FA Cup third-round tie against Wolves, Klopp provided an estimated timeframe for Van Dijk's return and described his absence as a significant setback.
"On Virg, it's a surprise and obviously a big blow, as he didn't feel a lot," Klopp said at Friday's pre-match press conference.
"I took him off actually, to avoid the risk, maybe he would have tried [to play on] and stuff like this.
"In the end, the diagnosis was pretty harsh. They talk about weeks – more than a month.
"We have to see how it goes but we have other centre-halves. Everything is okay for the team but for Virg, it's hard for him. He's played an incredible amount of games over the last few years.
"We cannot use him on the pitch, only off the pitch, so we will do that."
Asked whether the congested festive fixture list had caused Van Dijk's injury, Klopp responded: "It's his hamstring.
"He never had an issue with muscles or mentioned anything, between the games he was recovering.
"There's nothing to say about it, we did nothing different. It was one sprint."
As well as Saturday's meeting with Wolves, Van Dijk now appears likely to miss Premier League fixtures against Brighton and Hove Albion and Chelsea before the end of January.
Klopp will be desperate to have Van Dijk available for a crucial spell next month, in which Liverpool face Merseyside rivals Everton and fellow top-four contenders Newcastle United before playing the first leg of their Champions League last-16 tie against Real Madrid.