Liverpool centre-back Virgil van Dijk needs surgery on a knee ligament injury sustained in the 2-2 draw at Everton on Saturday.
The 29-year-old Netherlands defender was unable to continue following a rash challenge by Toffees keeper Jordan Pickford in the first half.
It is unclear how long he will be out for with the anterior cruciate ligament (ACL) injury.
He went for a scan before a specialist confirmed the extent of the injury.
Returning to action after ACL surgery can take many months.
Van Dijk has been a key figure for Liverpool since signing for them in January 2018 for £75m.
He has played every league game for the club in the past two seasons as Liverpool finished second in 2018-19 before winning their first top-flight title in 30 years in 2019-20.
The Dutchman was also a leading figure for the side as they won the Champions League in 2019 and Club World Cup later that year.
He had played seven times for the Reds this season prior to the Merseyside derby.
Van Dijk’s absence will leave manager Jurgen Klopp with regulars Joe Gomez and Joel Matip as his main centre-backs as well as the inexperienced Nathaniel Phillips.
Midfielder Fabinho can also deputise at centre-back as he did in the win at Chelsea earlier this season.
In addition to Liverpool, the Netherlands will be keeping their fingers crossed he will be fit to take part in the postponed Euro 2020, which is now set to take place from 11 June to 11 July 2021.