Virgil van Dijk will undergo knee surgery and is facing a battle to play again this season after scans confirmed that the Liverpool defender suffered an anterior cruciate ligament injury during Saturday's 2-2 draw against Everton.
Van Dijk was injured in the fifth minute of the 237th Merseyside derby following a challenge by Everton goalkeeper Jordan Pickford, which went unpunished by match referee Michael Oliver and VAR officials.
Although Van Dijk was able to walk off the pitch following treatment by the Liverpool physiotherapist, scans confirmed that the 29-year-old suffered cruciate ligament damage in the incident and, as a result, faces months on the sideline.
Liverpool sources have told ESPN that a timescale on Van Dijk's recovery period is impossible to gauge until the player has undergone surgery, but sources are reluctant to rule out a return to action this season.
The club has yet to set a date for Van Dijk's surgery because of the necessity for the swelling around the knee joint to subside sufficiently for the player to be operated on. Liverpool have also still to decide which surgeon will take charge of the procedure.
The loss of Van Dijk, a £75 million signing from Southampton in January 2018, is a major blow for Jurgen Klopp's Premier League champions, who begin their Champions League campaign with a trip to the Netherlands to face Ajax in Amsterdam on Wednesday.
Van Dijk has been a crucial presence at the heart of Liverpool's defence since arriving from Southampton and, until limping out of the Everton game, had played every minute of the team's 74 Premier League fixtures prior to the clash at Goodison Park -- a run dating back to September 2018.
He has also become a key figure for the Netherlands, and his injury means that coach Frank de Boer could be forced to plan next summer's Euro 2020 tournament without his most experienced centre-half.