The BVB coach has hailed the efforts of his players at the club's Switzerland training camp and says their physical conditioning has surpassed his expectations.
The German club ended last season on a disappointing note with defeat to Bayern Munich in the Champions League final, but Klopp's squad has refused to rest on its laurels during the summer break.
Klopp has taken his side to Austria for a training camp, where he and the club's fitness coaches have been able to assess the physical condition of the players before embarking on a gruelling schedule, but Klopp said he has been taken aback by their efforts.
"The fitness levels the players are showing are extraordinary and have allowed us to broaden training plans," Klopp told the BVB official website. "We sent the new players training plans, which they have been following after their holidays and their levels are good, too."
Klopp was also quick to stress the importance of the next seven days of preseason training, particularly with the new season looming large on the horizon.
"It´s the most important week of preseason. In Bad Ragaz we need to set the fitness levels and tactical disciplines for the coming season, because we have some huge challenges ahead of us."
Dortmund has been quick to bolster its squad following the loss of Mario Gotze to Bayern Munich, signing Henrikh Mkhitaryan from Shakhtar Donetsk and Saint-Etienne striker Pierre-Emeric Aubameyang.