City were blown away 3-0 at Anfield last Wednesday in the Champions League quarter-final first leg as Klopp's men ran riot in the first half before producing a performance of defensive steel after the break.
And on Saturday, Pep Guardiola's side were ready to celebrate winning the Premier League title at 2-0 up against Manchester United, only for their famous old foes to stage a thrilling second-half comeback to win 3-2 and spoil the party in stunning fashion.
Although domestic glory will still likely be theirs, City face an almighty task to turn around their first-leg deficit in Europe. But Klopp is all too aware that they have the weapons to hurt his side.
"No [City are not vulnerable]," Klopp told a media conference on Monday. "When we played City and we lost 5-0 [in September], everyone saw the quality of City, even though we were one man down.
"We all know about Pep, the best coach in the world, and it was clear they are outstanding, but there's no perfect football team in the world.
"You have moments, situations, days, sometimes only minutes, but they have been the most consistent, that's why they're champions at the end of the season.
Klopp on first leg: "It's our job to try with all we have to use that situation. We created it. The boys created it with an outstanding performance. Very, very mature. I'm excited and not anything else."— Liverpool FC (@LFC) April 9, 2018
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Klopp was asked if City's recent defeats gave other sides hope of catching them next season, to which he replied: "I don't think City will be worse next year. They're having an outstanding season but they are human beings, thank god.
"They had two results that maybe nobody really expected but we had to play our best to do that. The quality of the oppositions were strong - United were strong second half but I don't think too many teams should hope that they will have big problems next season.
"I'm excited about the opportunity, I'm really looking forward to the game. It's the best competition in the world.
"We are not more experienced than City players in this competition. We are trying our best to collect experience and tomorrow it's a big test for both teams and it'll be interesting to see."