His side were beaten 4-1 by Napoli in their opening Group A match, the Italians cutting them open at will in what was a woeful display from the visitors.
Liverpool have dropped points in four of their opening six Premier League matches too, and needed a 98th-minute winner against Newcastle to pick up only a second victory of the campaign.
It is a concerning run for Klopp, who just a few months ago saw his players competing on all fronts and taking their bid for an unprecedented quadruple into the final days of last season.
They host Ajax in Europe on Tuesday, in what will be their last match before the international break after this weekend’s clash against Chelsea was postponed due to policing issues ahead of the Queen’s funeral on Monday.
Klopp has reflected on the manner of that defeat to Napoli, believing it to be worse than anything he has seen since taking over at the club seven years ago.
“I watched the game back plenty of times and it was a real horror show to be honest,” Klopp admitted.
“It was the worst game we played since I was here. Eight out of 11 were below their level and the three others were not on a top level, just a normal game.
“I have to do something, I can’t sit there and wait for how we react. Is this the situation I wanted? No. But now you are in it you find it interesting and challenging.
“[We had a] general meeting, showing these situations and they are too obvious. It was not needed to say a lot about it but I did anyway.
“Did I question the players? Generally, no. In this situation, yes. ‘Why would you do that? Why would we do that?’.”
He added: “There are four or five days now of absolute truth. We didn’t hide anything, we didn’t hold back anything, there was no need for that. We just said it how it is.”