Goal understands the Viola will pay €3 million up front to hire the forward from the Serie A champions and can make it a permanent deal by paying a further €22m (£20/$25m) at the end of the season.
However, Juve have included a buy-back option in the deal worth €26m (£23m/$30m).
A cruciate ligament problem carried on into the start of 2017-18, robbing the winger of opportunities in the Bianconeri first-team until he was loaned to Schalke for the second half the campaign.
Although he was limited to just seven Bundesliga appearances, Pjaca was included in the Croatia squad for the 2018 World Cup, where he featured three times and made a cameo in the final against France.
After Gonzalo Higuain, Pjaca is the second attacker to leave Juventus following Cristiano Ronaldo's arrival, with youngster Andrea Favilli set to be sent out on loan to Genoa this season
Fiorentina, meanwhile, are expected to enhance their attacking options further wih the signing Kevin Mirallas from Everton.
The Belgium international, who returned to Olympiacos on loan in January, will also reportedly join on loan with an option for a permanent deal.