After a run of four consecutive wins and three in a row in the Premier League, the champions lost to bottom of the league Wolves who are in incredible form at the moment under Rob Jones.
Speaking after the game, Van Dijk revealed that Slot was rightly frustrated with his side who failed to jump into the top four.
"Yeah, he was angry. Of course. He had every right because we played poorly.
"That was already the case in the first half. Second half maybe there was more urgency but it still wasn't good enough. We have to pretty quickly turn this into full focus on Friday. That's our responsibility physically and mentally.
"Based on our performance up until they scored their first goal, we deserved to go 1-0 behind. We were very poor.
"We were too slow and predictable in possession. We made the wrong decisions. We didn't concede any big chances up to that point. Defensively, we were still solid.
"But towards the end, when the game started to open up, any team can become dangerous and that's what happened."
The Reds return to Wolves on Friday night for an FA Cup fifth-round tie as they seek revenge in what will be a tough test for the side who looked clueless on Tuesday night.
Manchester United, Chelsea and Aston Villa all play on Wednesday night and could extend their lead on Liverpool whose Champions League dreams could be in tatters. Liverpool next face Tottenham in the Premier League, another side close to relegation.