The 46-year-old is hoping his side get back to winning ways in the Bundesliga but does not expect a straightforward victory at the Signal Iduna Park this weekend
Die Borussen overcame 1860 Munich 2-1 in extra time in the DFB Pokal on Tuesday but were held to a 1-1 draw last weekend at Nurnberg, on the back of suffering a 2-1 Champions League defeat to Napoli.
Despite sitting in 17th place in the Bundesliga, Freiburg have lost just once in their last six matches and Klopp feels they will pose a tough challenge.
“Freiburg are a lot better than their table position would suggest,” he told reporters.
“They are doing a great job in Freiburg, even if it has taken a while. It looks a lot like Freiburg football again.”
A busy fixture list and injuries to many key players has left Klopp with a selection dilemma but Dortmund will welcome back Marcel Schmelzer from injury against an energetic Freiburg side.
“Freiburg has racked up the most kilometres so far. We will need to run a lot, invest a lot of energy and play a lot of football," Klopp added.
With Ilkay Gundogan still unavailable with a back problem, Sven Bender and Nuri Sahin look set to continue at the base of Dortmund's midfield this weekend.