Per Italian source Gianluca Di Marzio the loan fee is €500,000 (£445,200) with an option to buy for €7m (£6.2m).
The Belgian winger was back in the news earlier this week after being named as one of four players who were asked to train away from the main group. Ashley Williams, also in that group, was shipped out on Thursday to Stoke City also on loan. Nikola Vlasic has also been linked with a loan move with Newcastle interested while Cuco Martina rounds off that group.
Mirallas had an undistinguished half-season at Everton last year, getting into a spat with caretaker manager David Unsworth during training, before getting loaned out to his former side Olympiakos.
While he was welcomed back to Greece by baying crowds, the same adoring fans soon turned on the underperforming player who ignominiously saw his loan deal terminated with just a couple of weeks left in the season.
Everton are still paying the price of handing the player a new three-year contract at the end of the 2015-16 season and unless he hits it off with Stefano Pioli at Fiorentina and La Viola decide to exercise their buyout option, Mirallas will unfortunately be back again next season.