Jurgen Klopp questioned the decision to award Everton a late penalty that condemned Liverpool to a 2-0 defeat in the Merseyside derby at Anfield.
Carlo Ancelotti's visitors sealed a first win at the home of their near neighbours in almost 22 years on Saturday thanks to strikes from Richarlison and Gylfi Sigurdsson.
It was Sigurdsson's 83rd-minute spot-kick, after Dominic Calvert-Lewin was adjudged to have been fouled in the box, that most irked the losing manager.
Referee Chris Kavanagh was asked to inspect the incident at the pitchside monitor but stuck with his original decision, much to Klopp's dismay.
Asked about the incident at his post-match press conference, the Liverpool boss said: "I really think it's unfair to ask me because everybody asks me, which means everybody thinks it was not a penalty.
"But that's not really important because the ref thought it's a penalty. I wanted to talk to him after the first few interviews I had but he left already.
"I [wanted to ask] what did he see? Because the VAR calls you over in a situation like that, then I think he is in doubt about the decision.
"But he needed only a second; he went there, watched it from three, four yards and, yeah, penalty.
"He saw, obviously, something all the people didn't see. I didn't see it back yet but everybody who sees it tells me the same: 'How can it be a penalty?'"
As they contend with the disappointment of derby defeat, Liverpool must also count the cost of yet another injury blow following Jordan Henderson's first-half withdrawal.
On his captain, Klopp added: "It's the groin/adductor region and nobody in the medical department was kind of positive about it.
"So, it doesn't look good but we have to wait for the scan tomorrow, hopefully."
As for the game as a whole, Klopp highlighted an early moment of defensive sloppiness and profligacy at the other end of the pitch as the reason for Liverpool's downfall.
Asked about how much the result had hurt, he said: "A lot. A lot. But we conceded a completely unnecessary first goal, let's not forget that, and that's a big part of the game.
"There are two big parts, you have to defend and you have to score, and in one situation we didn't defend well enough so they could score.
"We made a mistake, if you want. And we didn't use things we created and that's why we have the result."