The tackle by Everton keeper Jordan Pickford which left Liverpool's Virgil van Dijk needing knee surgery was "completely stupid", says Reds midfielder Georginio Wijnaldum.
Van Dijk suffered an anterior cruciate ligament (ACL) injury in the challenge - which went unpunished - and is set to miss at least most of this season.
Wijnaldum said "none of the players slept" after what happened on Saturday.
Manager Jurgen Klopp said his feelings were "similar to my players".