Fiorentina reportedly want to insert a €12m (£10.3m) buyout clause in Adem Ljajic's new contract, which will only be available to teams outside of Italy.
The measure is believed to be a result of AC Milan's approach for the Serbian international, who is entering the final year of his contract at the Stadio Artemio Franchi.
Rossoneri vice-president Adriano Galliani confirmed that a bid of around £6m was lodged last week - an offer that was flatly rejected.
The Viola have opened themselves to the possibility of losing Ljajic, who scored 11 goals in Serie A last season, should he fail to agree new terms this summer.
However, La Gazzetta dello Sport report that they are pulling out all the stops to prevent the 21-year-old moving to the San Siro by offering him a five-year contract worth around £1.3m per year - which includes the buyout clause for foreign clubs.
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