The Italy international has been out of action since January with knee ligament damage but has returned to full training and looks set to feature at the Stadio Olimpico
The striker has not played since suffering knee ligament damage against Livorno in January but has now returned to full training.
Montella freely admits that Rossi is not yet match fit but is nonetheless hoping to call upon the Viola's top scorer for the game at the Stadio Olimpico, particularly as fellow forward Mario Gomez is set to miss out through injury.
"Rosi is training," the former Roma boss confirmed. "I do not know how many minutes he has in his legs but the desire to call upon him is definitely there.
"Gomez? The reality is that he's not training with the group. His inclusion is fairly unlikely."
Montella is aware of the significance of the game for Fiorentina, whose last major title was the 2001 Coppa Italia.
However, he says that the Viola, who are currently fourth in Serie A, must invest further in his squad this summer, regardless of the outcome of the game.
"We know that the result of this game will change how our season is judged," he admitted. "But I hope that the outcome of the game does not decisive for the club and our intentions in the transfer market."
Napoli are also desperate for silverware, after seeing their anticipated title challenge fade away. But Montella says that the Partenopei are clearly moving in the right direction under Spanish coach Rafa Benitez.
"Napoli have nothing to prove," the ex-striker argued. "They have already got more points in Serie A this season than last.
"They have more work to do to reach the top but they are doing very well. Next year they will definitely be even better.
"Benitez is a world-class coach. He's growing Napoli and he's also a very nice person."