Klopp: We need to close the gap
Dortmund have picked up just seven points from their first five league games this season and were shocked 2-1 at home to Hertha Berlin last weekend, having also lost at Hoffenheim on 13 August.
With Bavarian giants Bayern Munich setting the early pace in the German league, Klopp says his team must win at Hannover with the champions 11th in the table before today's matches.
"Because we lost to Berlin, the gap is starting to grow and we are lagging behind by two or three points," Klopp told Bild. "We need to correct this in the coming weeks. The distance should not be allowed to become too big."
Germany midfielder Mario Gotze will miss tomorrow's game as he completes a two-match ban after being sent off against Bayer Leverkusen at the end of August.
Fellow midfielder Sven Bender is also missing with injury and Klopp says injuries and suspensions have taken their toll and prevented him from fielding a settled side.
"It is a special situation," he said. "On the one hand, we have only seven points, which doesn't feel so great. On the other hand, we have had to change almost our entire midfield."
Dortmund drew 1-1 at home to Arsenal on Tuesday in their opening UEFA Champions League match.