Virgil van Dijk has undergone successful surgery on the knee injury that could see him miss the remainder of the 2020-21 season.
Centre-back Van Dijk damaged ligaments in the early stages of the Merseyside derby on October 17 following a challenge from Everton goalkeeper Jordan Pickford.
“The Liverpool defender’s planned operation took place in London and was conducted successfully," a statement on Premier League champions’ website read.
"Van Dijk will now immediately focus on the beginning of his rehabilitation with the support of the Reds' medical department. No timeframe has been placed on the Dutchman’s return to action.”
The former Celtic and Southampton player was pivotal in helping Liverpool end their 30-year wait to be crowned domestic champions again, scoring five goals as he played in all 38 league games last season.
Van Dijk's absence has been further compounded by injuries to team-mates Joel Matip and Fabinho, the latter having been pushed back to play in defence due to a lack of alternative options available to Jurgen Klopp.
Brazilian Fabinho came off with a hamstring issue during the first half of the Champions League victory over Midtjylland on Tuesday.
Rhys Williams, 19, came on to partner Joe Gomez and could be set for a Premier League debut when Liverpool host West Ham on Saturday. He was the subject of praise from Klopp and team-mate Trent Alexander-Arnold after his display against the Danish side.
However, Klopp has also highlighted 23-year-old Nathaniel Phillips and Billy Koumetio, 17, as options to slot into the back line.
The Hammers, meanwhile, have suffered an injury setback of their own, however; Michail Antonio will miss the game at Anfield with a hamstring problem.
Antonio has scored 11 goals in his past 13 Premier League games and has managed 39 in the competition in total. Only three players - Paolo Di Canio (47), Mark Noble (46) and Carlton Cole (41) - have registered more for the club in the competition.
David Moyes’ side are 12th in the table after six matches, five points behind Liverpool, who are in second place.