Champions League qualification is the sole objective for BVB this season, according to the director, who is determined to keep expectations under control at the club
Bayern Munich have dominated the German top-flight in recent years, topping the table for four successive seasons.
Dortmund have lost Mats Hummels to the Bavarian giants, while Henrikh Mkhitaryan and Ilkay Gundogan have moved to Manchester United and Manchester City respectively.
Andre Schurrle and Mario Gotze have been the headline arrivals at Signal Iduna Park, but Zorc is not expecting Dortmund to push Bayern, who beat Thomas Tuchel's side in the DFL-Supercup on Sunday, for the title.
"Of course we are not yet at the level where we want to be," Zorc said on Eurosport following Dortmund's 3-0 friendly win over Sandhausen on Monday.
"It would be presumptuous to always expect a title. Our objective remains Champions League qualification.
"We will try to make this season the best we can with our conditions.
"We believe that we are well equipped for the start of the season."