On 28 August 2013, Rebić signed a five-year contract with Italian side Fiorentina, for an undisclosed fee. Upon passing the medical exams, he was given the number 9 shirt. He made a debut on 30 September, coming on as a 36th-minute substitute for injured teammate Giuseppe Rossi, in a 2–2 home draw against Parma. During his debut he sustained an injury, causing him to be sidelined for three weeks. Rebić made three more appearances for Fiorentina before he scored his first goal on 8 January 2014, starting and scoring the second goal of a 2–0 Coppa Italia last-16 home win against Chievo Verona. On 18 May, he scored his first goal in Serie A in 2–2 draw against Torino at the Stadio Artemio Franchi, two minutes after replacing Manuel Pasqual.