Zorc admitted he's a fan of the City striker earlier this week, but hinted on Friday that the price tag could still be a stumbling block.
Dortmund appear resigned to losing top scorer Robert Lewandowski at the end of the season, and Dzeko has been identified as a possible replacement.
But the Bosnian international, who cost City £27m when he signed from Bundesliga club Wolfsburg, may be a little too expensive for Zorc's club.
Speaking to German newspaper Bild, Zorc said: "There should be little doubt about Dzeko being a top-class striker. 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."
Dzeko is City's joint second top scorer this term with 13 goals, despite playing a reduced role from the bench. Carlos Tevez and Sergio Aguero have been preferred to Dzeko on various occasions this season, and he may seek first-team football elsewhere next term.
Dortmund forward Robert Lewandowski has been linked with City's rivals Manchester United, and with his contract set to expire at the end of next season, Dortmund may decide to cash in this summer.
The reigning Bundesliga champions progressed to the Champions League quarter-finals earlier this month, and will play Malaga.
They had faced Manchester City in the group stages, securing a 1-1 draw at the Etihad Stadium and a 1-0 home win in Germany.