Rossi signed from Villarreal in January as he recovers from knee surgery.
"Giuseppe's mood has remained high," Andrea Pastorello told Sky Sport Italia. "Even during the long period of injury.
"He is a balanced boy and is happy to be back in Italy.
"We have finally arrived and he hopes to be able to do his best on the field.
"Montella wanted him to be in Florence, and we're happy."