Liverpool face the prospect of being without Virgil Van Dijk for several months after it was confirmed their key defender requires knee surgery – but they are reluctant to rule him out for the season.

News of anterior cruciate ligament damage to the 29-year-old, sustained in a controversial high challenge by Everton goalkeeper Jordan Pickford in Saturday’s 2-2 Merseyside derby draw, is the nightmare scenario for the Reds.

“Following surgery, Van Dijk will begin a rehabilitation programme with the club’s medical team to enable him to reach full fitness as soon as possible,” a club statement said.

Not only does the injury rob them of one of their most influential players for the majority of their Premier League title defence, but also leaves Liverpool with just two senior centre-backs in Joel Matip, who has been plagued by niggling injuries himself, and Joe Gomez.

Jurgen Klopp opted not to replace Dejan Lovren when he left for Zenit St Petersburg in the summer and was content to gamble on utilising midfielder Fabinho as cover.

The damage suffered in his clash with Pickford, for which the Everton goalkeeper escaped punishment due to VAR official David Coote overlooking the tackle after ruling on the Holland captain’s offside in the build-up, means Van Dijk will have to have an operation.

However, club sources are unwilling to write off his season just yet, considering the player’s previously excellent fitness record, and remain hopeful he can still play a part in the campaign at some point.

Van Dijk released a statement on Sunday night in which he vowed to come back stronger than ever.

“This afternoon I met with a leading consultant to start the process of planning the finer details of my rehabilitation following the incident yesterday,” he posted on Twitter.

“I’m now fully focused on my recovery and will do everything I can to be back as quickly as possible.

“Despite the obvious disappointment I’m a firm believer that within difficulty lies opportunity and with God’s help I’m going to make sure I return better, fitter and stronger than ever before.

“In football, as in life, I believe everything happens for a reason and it’s important to try and keep level headed whether going through the highs or the lows. With the support of my wife, kids, family and everyone at Liverpool, I’m ready for the challenge ahead.

“I’d like to thank everyone for the messages of support, it’s meant a huge amount to me and my family, and I’ll now be doing everything possible to support my team-mates in any way I can ahead of a big few weeks ahead as I take my own recovery day by day. I’ll be back.”

The injury leaves Klopp with an immediate headache as he faces having to field the untested pair of Matip, whose return in the Merseyside derby was his first appearance since the opening day, and Gomez, who was dropped at the weekend after some recent patchy form.

The 23-year-old Nat Phillips, with just one FA Cup appearance to his name either side of two loan spells at Stuttgart last season, is now the back-up option, with the highly-rated but unproven 17-year-old Billy Koumetio another alternative.

Liverpool’s defence has looked leaky already this season, conceding 13 goals in five matches, including seven at Aston Villa, with Van Dijk in the back four, so his absence for any length of time would raise real questions about their chances of staying the distance in a title race.

Klopp, however, was keen to throw his backing behind Gomez after a shaky couple of weeks.

“The set-piece (for Everton’s first) was unlucky because Virgil was not on the pitch, we sorted it in the game but it was the first corner when he was not on the pitch,” he said.

“Joe Gomez played a sensational game, a good game. I am not worried about the boys.

“The problem we have at the moment is that I am not really in a good mood, I have injured players in the dressing room and that is not good.”

The news on midfielder Thiago Alcantara, who also went for a scan on a knee problem sustained in the tackle which saw Richarlison sent off late on, is slightly more promising.

Liverpool have to wait for the injury to settle but are optimistic it is not serious, although their £20m summer signing from Bayern Munich is unlikely to feature this week against Ajax.

The club have lodged a request with the Premier League asking for a review of the Merseyside derby VAR decisions.

They have asked why Pickford’s challenge on Van Dijk was not considered for a red card just because the Dutchman had been ruled offside by a replay and also for an explanation on the mechanics which saw Sadio Mane ruled offside in the build-up to what would have been a Jordan Henderson added-time winner.

Liverpool are also understood to be concerned by the confusing and contradictory messaging emanating from the Premier League.

While not calling into question of the integrity of officials, the club believe it is crucial to have more transparency around how and why the outcomes were determined for the integrity of the game for everyone and the safety of players. Conflicting versions of events, it is understood, have left Liverpool officials deeply troubled.