The German club are wary that the English champions could price them out of a deal for the £27 million striker, who previously enjoyed a prolific spell in Germany with Wolfsburg.
The Bosnia international could be set to leave the Etihad Stadium in the summer after failing to secure a first-team spot ahead of Argentine pair Sergio Aguero and Carlos Tevez.
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"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."
The Champions League quarter-finalists are on the lookout for a new striker as Polish forward Robert Lewandowski is set to leave the club in the summer after opting against signing a new contract. His current deal expires in 2014, and City's rivals United are rumoured to be interested.