Frankfurt held the defending champions to a 3-3 draw at the Waldstadion in the reverse fixture, but not only that result has warned Klopp about the newly-promoted sides strength.
"I cannot recognise any sign which suggests they are going to suffer a collapse," said Klopp.
"Frankfurt are playing an incredibly good season. The way they turn defence into attack is excellent, and they have an Alex Meier who is having what seems to be the 47th second wind of his career.
"It is going to be a tough task for us."
A suspension for Robert Lewandowski makes the challenge even greater for Dortmund and Klopp has yet to decide how to replace the Poland international, his side`s top goalscorer this season.
"I have a few options in my head," he said. "But I am not going to reveal them yet.
"We will find a solution, and whoever it is enjoys our full faith."
Julian Schieber is the most natural choice, but Maro Reus or Mario Gotze could be moved forwards, as they have been for Germany recently.
That is the least of Frankfurt coach Armin Vehs concerns, though.
"It is not like we can choose who we want to play for them, so I'm not really thinking about it," he said at a press conference.
Veh can only choose his own 11 players, and those are likely to be similar to the ones who took to the field in the 3-3 draw last September.
Indeed, only one change is necessary since Erwin Hoffer is no longer at the club, and Srdjan Lakic is set to replace him.