Zollner worked with the Bundesliga outfit between 1992 and 2009, where he saw the club win two league titles and a Champions League trophy.
Klopp on the other hand coached Dortmund from 2008 to 2015 before moving to the Premier League to coach Liverpool.
Zollner worked with Klopp for a short time at the Signal Iduna before moving on to Bundesliga two side VFL Bochum.
The German has labeled his compatriot a ‘special guy’ but insists the 52-year-old was arrogant sometimes.
"He's a special guy,” the 52-year-old told Goal and SPOX of Klopp.
"There were so many days when you'd think: 'Great guy!', but sometimes you'd think: 'what an egocentric!’
"One time, Jakub Blaszczykowski called me when he was coming back from the [Polish] national team. He said he couldn't train because of a muscle injury but would still come to the team meeting.”
"Before the meeting, I went to Klopp with Kuba (Blaszczykowski) and told him what was going on. He then went pretty crazy, probably because he had only just learned about Kuba's injury at that moment. “
"Zeljko Buvac (Klopp's former assistant) would often appear at such moments and say: 'Kloppo, smoke a cigarette now and calm down!’ He was one of the best assistant coaches I've ever worked under.”
“But Kloppo had the balls to apologise when the way he treated someone was too much.”
