Kiessling has scored a hatful of goals this season.
"We have turned down an official enquiry from Fiorentina for the services of Kiessling," Holzhauser told Express. "We turned this down immediately.
"Stefan Kiessling is under contract until June 2015. We plan to sit down and discuss a new contract this summer.
"I would like to see him retire from the game as a Bayer Leverkusen player one time in the future.
"We cannot afford to lose Stefan Kiessling if we want to have a successful next season."