Third-placed Dortmund will climb above Leverkusen in the Bundesliga with a victory on Saturday, but have just one win from their last three league fixtures.
And Klopp knows he will be up against a formidable opponent, with Leverkusen having lost one of their last 10 league matches.
"Leverkusen have become result machines, incredibly strong," he said. "They are always dangerous at set-pieces.
"Both Leverkusen and we are struggling with ...
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