Rossi joined the outfit on Friday from Villarreal.
"I would have made this move sooner, even last summer," the player, who has reportedly cost an initial 10m, stated.
"I'm happy to be at Fiorentina. They are the only side who came forward with facts and not just with words. That was very important to me.
"I like the Viola project, a lot. I want to be a part of it. There are many youngsters here, but also players of experience. And we all know that Fiorentina are playing the best football in Italy.