Jurgen Klinsmann is making the Hertha Berlin players suffer in training to get them fit for the Bundesliga relegation battle, forward Davie Selke says.

Hertha forward Selke told German magazine Kicker that Hertha are feeling "the fire in every training session. We are running further than we used to" ahead of their league clash at Eintracht Frankfurt on Friday.

"We are currently suffering, but we like to suffer," added Selke, who had a second-half equaliser against Dortmund ruled out for offside by VAR.

Klinsmann, who has coached Germany and the USA at World Cup finals, took charge a week ago with Hertha fighting to avoid a third relegation from the German top division in a decade.

Hertha currently sit in 16th -- the relegation playoff spot -- and just three points from the automatic drop zone.

Klinsmann began last Saturday with a 2-1 home defeat to Borussia Dortmund, who played the second half a man down after 2014 World Cup winner Mats Hummels was sent off for two first-half yellow cards.

The former Inter Milan and Bayern Munich striker has brought in a new fitness coach Werner Leuthard in order to bring his side up to speed.

"What he does with us is intense. I felt extremely fresh and fit. We have already noticed how that helped us," said 24-year-old Selke.

After five straight league defeats, Klinsmann said it is "important that we strengthen the self-confidence of the team" and describes Leuthard as a "warhorse with decades of experience in the Bundesliga".

Klinsmann, who won both the World Cup and the European championships during his career, has former Werder Bremen boss Alexander Nouri as assistant coach, as well as former Germany defender and Hertha captain Arne Friedrich as performance manager.

With four defeats in their last five games in all competitions since beating Bayern Munich 5-1 in Frankfurt in early November -- which cost Niko Kovac his job as Bayern coach -- Eintracht need a win to halt their drop down the table.