Borussia Dortmund coach Jurgen Klopp is trying to put on a brave face as his team prepare for the daunting trip to Werder Bremen.

Thomas Schaaf's men have not lost a match since August 8 with Dortmund the latest in a long line of clubs attempting to break that success at the Weser Stadion.

Although his side have also put together a good run of late with 10 points from their last four matches, Klopp fears that may come to an end.

"We haven't played sensationally in these games, but still enough to prevent our opponents from letting their own strength get the better of us," he said.

"It is going to be a huge challenge for us to survive in Bremen."

Klopp has been hit by numerous injury absences in training this week which have forced him to improvise.

Nuri Sahin, Kevin Grosskreutz, Markus Feulner and Jakub Blaszczykowski have all now returned to training, but that does not mean they will be available.

"It's not been a good week," admitted Klopp.

Bremen may not be at full strength either as Claudio Pizarro is still sidelined through injury, and Schaaf thinks he will "probably not be available on Sunday".

"Claudio plays an important role in our game with his experience and his quality, but above all the self-assuredness that he emits," added Schaaf.

"Obviously I would have preferred him to be with us on Sunday."

Aaron Hunt, who this week received his first call-up to the Germany national team, is fit, even if he says the battery levels are running a little low.

"I think this will be our seventh match in the space of three weeks and that obviously costs energy," he said on the club's website.

"Nevertheless, we want to go as far as we can in all three competitions."

Given his international call-up, Hunt can now look forward to two more games in the next 10 days as the national team faces Chile and the Ivory Coast, but that will be an acceptable downside to his first experience with the Germany squad.