"Mats Hummels is the best German defender" - Michael Zorc

Hummels, 30, rejoined Dortmund earlier this summer after spending three years at Bundesliga rivals Bayern Munich, where he added three successive Bundesliga titles to the two he won in his first stint at BVB between 2008 and 2016.

"For me, Mats is the best German defender," Zorc told German broadcaster Sport1. "We expect him to take on a leading role on the pitch. That's why we signed him."

Watch: A reminder of what Mats Hummels brings to the table

Hummels joined Dortmund from Bayern in 2008 - initially on loan - and went on to make 309 appearances for the club. After winning his first Bundesliga title in 2010/11, he claimed a league and DFB Cup double the following campaign before getting his hands on the 2014 FIFA World Cup with Germany.

He returned to boyhood club Bayern in summer 2016, playing in 118 matches in all competitions, including 33 in 2018/19 as the record champions pipped Dortmund to the Bundesliga title on the final day.

Zorc now hopes Hummels and Co. can go one better in 2019/20.

"Last season is massive motivation for us," he said. "We're obligated to build on it."

Dortmund resumed pre-season training on 3 July. The Black-Yellows travel to the USA on 15 July, with their first competitive fixture of the new campaign coming against Bayern in the German Supercup on 3 August.

After travelling to Uerdingen in the DFB Cup first round (9 August), last term's Bundesliga runners-up begin their pursuit of a first league title since 2012 at home to Augsburg (17 August).