The Bosnian has guided Aquile into third place in Serie A after taking over from Edoardo Reja in the summer.
"[Petkovic] has proved himself to be a great coach," Football Italia quotes Montella as saying.
"He's a really balanced individual, he has a good way of working and he has adapted well to Serie A. He has some great footballing ideas and charisma too.
"Lazio are a complete side, but I don't know whether we are on the same level as them right now."
Fiorentina are sixth in the table.