The 46-year-old 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 Signal Iduna Park club ended last season on a disappointing note with defeat to Bayern Munich in the Champions League final, but Klopp's squad have refused to rest on their laurels during their summer break.
Klopp has taken his side to Austria for a pre-season 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 the former Mainz boss admits he has been taken aback by their efforts.
He told the club's official site: "The fitness levels the players are showing are extraordinary and have allowed us to broaden training plans.
"We sent the new players training plans which they have been following after their holidays and their levels are good, too."
The 46-year-old was also quick to stress the importance of the next seven days of pre-season training, particularly with the new season looming large on the horizon.
"It´s the most important week of pre-season. 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 have been quick to bolster their squad following the loss of Mario Gotze to Bayern Munich, signing Henrikh Mkhitaryan and from Shakhtar Donetsk and Saint-Etienne striker Pierre-Emeric Aubameyang.