The 25-year-old, who joined Viola from Palermo in the summer, started in last night's Europa League clash with Pacos de Ferreira, although he was subbed for Oleksandr Yakovenko after 74 anonymous minutes in Portugal.
Ilicic scored 10 goals in Serie A last season, but is yet to find the net in eight appearances this term.
However, Montella said that the Slovenian international is still struggling for fitness, and expects his performances to pick up soon.
"He needs to play, as this cannot be the Ilicic we know," he told Sport Mediaset.
"He has been unlucky so far with the Viola, as he arrived with a few fitness problems and picked up another injury straight away.
"This slowed down his process of settling into the team, but we will soon see him in his best shape."
Last night's goalless draw was the first time that Fiorentina dropped points in the Europa League this season.