The Manchester City striker has been linked with a move to BVB and the club's sporting director would like to see a transfer happen
The Bosnian has been mooted as a potential replacement for Robert Lewandowski, who is likely to leave the German champions in the summer.
But the Schwarzgelben are insistent that they cannot do a deal for Dzeko if the Premier League champions are unwilling to set a realistic transfer fee.
"There should be little doubt about Dzeko being a top-class striker," Zorc told Bild.
"He is a great forward and a player one should be keen on. However, there is also still somewhat of an economic aspect.
"[A transfer] would be down to pure maths because Dzeko is under contract at Manchester City beyond the end of the season."
Despite scoring 13 goals in all competitions this season, Dzeko has struggled to hold down a regular place in the Citizens' first team.