Jurgen Klopp has criticised his forward players for a lack of defensive effort following the Reds' thrilling win over Manchester City earlier this month.
Liverpool pressed the Premier League leaders on their way to an impressive 4-3 victory at Anfield two weeks ago.
However, they stumbled in the subsequent matches, first losing at last-placed Swansea in the league and crashing out of the FA Cup against West Brom over the weekend.
When asked on Monday if his team suffered from overconfidence following the City triumph, Klopp told reporters: "I don't think so. But if you want, since then our offensive positions didn't defend as well as then, for example. That's the truth.
"These boys, we know potential-wise are world class. But real world class is to bring it on the pitch again and again and again.
"We had two completely different games, but especially against West Brom compared to Swansea, we needed all positions to be involved in defending.
"West Brom was not only the most experienced team age-wise that's ever played, they had quality with [Jay] Rodriguez, if he wasn't injured for two years he'd be on another level and he is in a good moment for West Brom. [Hal] Robson-Kanu, hard workers in midfield, [Chris] Brunt crosses from everywhere, so they are a good team.
"From that, you need to defend really in a compact formation. We were not compact. That's the problem.
"When they played a pass for the first goal, we lost two challenges, that's not cool. We could have defended it already. The second one is just, as a group, no good defending.
"We need to find out whether it's a misjudgment of the City game. I don't think so. But if it was, that needs to be finished."