Virgil van Dijk received the devastating news earlier this week that he had torn his ACL.
The Dutchman will have to undergo surgery and is expected to be out for the remainder of the season.
Van Dijk's injury means Liverpool are now very light in the centre of defence.
Joe Gomez and Joel Matip are Liverpool's only two first-team centre backs following Dehan Lovren's departure last summer.
Fabinho could be used for cover - he has shown in the past he can fill in - but that's far from ideal.
And elsewhere, Jurgen Klopp can call upon youth players Rhys Williams, Sepp van den Berg or Nat Phillips.
To be honest, Klopp doesn't have many options at his disposal.
The German has reportedly recognised that it is now an area of weakness and is willing to buy a centre-back in January.
And, according to James Pearce of the Athletic, per sportsmole, he has already identified two possible targets.
Their top option to buy in January is said to be Brighton's Ben White.
The Brighton defender was hugely impressive in the Championship last season at Leeds United.
Marcelo Bielsa's side tried desperately in the summer to buy him. They submitted three offers - with the third believed to be worth £25m - but Brighton weren't tempted to sell.
It seems likely that Liverpool will have to put in a much bigger offer should they want to sign the highly-rated youngster in a few months time.
If they can't seal a move for White, it is believed they will target Schalke's Ozan Kabak.
The 20-year-old defender is one of the most highly-rated youngsters in the world.
He impressed in the Bundesliga for Schalke last season, featuring 26 times in the league.
It is believed that the German club will want around £40m for his services, though.
So plans are in motion at Liverpool to replace Van Dijk. It appears they will have to spend big if they want to bring in one of their top targets, though.