The Brazilian is expected to leave Loftus Road this summer, although strong links with Napoli and Arsenal appear to have gone cold.
Viola are the latest team rumoured to be interested in the former Inter Milan stopper but Cardoso - and the club - maintain that there have been no discussions.
"QPR would have no problem letting him go to Fiorentina - or to any other club - but if the €3.2m (£2.7m) does not arrive then it's difficult to close the deal," Cardoso told Radio Blu.
"The move can only be made if we are offered a four-year contract. He has a contract with QPR until 2016, so it has to match that date. The length of the contract could compensate for a difference in wages, but if it expired earlier than 2016 then it would be pointless.
"Julio Cesar likes Fiorentina, so they could be the right team for him to target a World Cup spot. I never had contact with Fiorentina, but I did send a close friend to speak to the Viola. For now there is no news."
The 33-year-old joined the Hoops last August.