The decision to let the tackle go unpunished during the game led infuriated Liverpool fans to voice their disgust online, and even triggered an attempt to protest the decision with a march.
The whistle had already been blown for offside when Pickford scythed down Virgil Van Dijk in the box.
Although Liverpool have not yet made any statement about Van Dijk's condition, he was pictured leaving hospital on crutches on Saturday evening.
In an Instagram post on Sunday night, the defender said: "I'm now fully focused on my recovery and will do everything I can to be back as quickly as possible". Many predict he is unlikely to play again this season.
"To be honest, I never saw it".
One courageous Reds fan even went as far as to promise his "mate" van Dijk he would "get" Pickford for him, swearing he would bump into England's accident-prone number one, much to the ridicule of social media users. Then we obviously saw that the flag was up, so offside. "I still thought it was worth a look on the foul but that didn't happen", commented Klopp.
"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". "What can I say?"
Up to that point Van Dijk had not missed a minute of Premier League action since September 2019 and his influence on the team has been instrumental in them winning the Champions League and Premier League in the last two seasons.
The Dutchman faces a lengthy spell on the sidelines and his absence could put a huge dent in Liverpool's hopes for a successive Premier League title.
The powerful defender has damaged his anterior cruciate ligament, and won't be returning for months now.
Klopp will now decide whether to play the 29-year-old, who has only recently returned from an injury setback, amid a busy week for the Premier League champions. Zlatan Ibrahimovic's Manchester United career was effectively over after he picked up the ACL injury during their Europa League clash with Anderlecht in 2017.