The strike duo combined well to beat Werder Bremen keeper during Wednesday's match in the German Cup round of 16.

Frei put the home side ahead early on 11 minutes from a close-range shot after latching onto a deft pass from Egyptian forward Zidan.

"It was great," Dortmund official website quoted Klopp as commenting on the harmony between Zidan and Frei.

Bremen eventually won 2-1 as Klopp urges his side to make up for the cup exit when they play Leverkusen in their first match after the Bundesliga winter break.

"We need to concentrate more and find greater consistency to beat Leverkusen," Klopp added.

Zidan and Frei scored four goals each this season. Defender Neven Subotic is Dortmund’s top scorer with five league goals.

Injury List

Klopp will have to do without injured quartet Sebastian Kehl, Dede, Mats Hummels and Jakub Blaszczykowski as well as the suspended Tamas Hajnal.

"We can't do anything about the long list of absentees. We have to throw everything available into this game," Klopp stated.

Dortmund lie sixth in the Bundesliga table with 29 points, three behind fifth-placed and next opponents Leverkusen.

Watch Zidan's assist against Bremen