A 1-1 draw between Napoli and Paris Saint-Germain in Group C's other game on Tuesday means just two points separate the four teams heading into the final two matchdays.
There were plenty of candidates for worst player, but Daniel Sturridge's terrible first half performance was noticeably awful.
"I saw, unfortunately, a few games like this already and it's really hard to find your mojo back", surmised Klopp as Belgrade rocked to Red Star's first win in the competition for 26 years.
Liverpool ideally need to get a result with a tricky tie away in the French capital to come next before a potential qualification decider at home against Napoli at the end of the group.
A poor performance against Red Star Belgrade in the UEFA Champions League resulted in many counting on what went wrong for Liverpool. We had moments, we had kind of nearly-chances, the biggest in the last two three minutes and before that not enough.
Liverpool midfielder James Milner told United Kingdom broadcaster BT Sport that Liverpool had problems "all over the field" in the first half and never properly recovered.
Forward Milan Pavkov headed his side into the lead after 21 minutes and fired a powerful effort into the bottom corner to make it 2-0 shortly afterwards.
Liverpool had the briefest of openings, but, uncharacteristically, Adam Lallana's first touch let him down as he tried to control Salah's square pass inside the penalty area. They scored a goal and then completely out of the blue they scored a second and the atmosphere completely changed.
The fan said: "It would even be understandable if it was Marko Grujić because he used to play for red star but it seems like Markovic is doing it as a dig at the club. we should just cut our losses and terminate his contract".
Almost three decades on, Red Star don't have a household name in their squad and needed to qualify for the group stage through the playoffs.
Milan Pavkov scored a first half brace for Red Star Belgrade.
Speaking of the Switzerland international's situation, the manager said, "We have heard and read the speculation and talk about what kind of reception Shaq would receive and although we have no idea what would happen, we want to go there and be focused 100 per cent on football and not have to think about anything else, that's all".