The Roma striker has a muscle problem and coach Giovanni Trapattoni has called-up uncapped Chievo Verona forward Massimo Marrazzina.
Montella joins a long list of injury victims as Francesco Totti, Gianluca Pessotto, Gianluca Zambrotta, Cristiano Zanetti, Christian Vieri and Francesco Toldo have all been forced to sit out the game with Slovenia.
The game will also see a new captain as the previous keeper of the Azzurri armband - Paolo Maldini, has now retired.
Internazionale's Fabio Cannavaro will take over as captain for the game, although it is not yet known whether he will be Maldini's permanent successor.
"I feel a great responsibility in wearing the captain's armband," he told the Gazzetta dello Sport.
"It is especially important to me because I truly believe in my heart that representing my country is something you should not take lightly."
The game will also see an international debut for Juventus's Under-21 star Matteo Brighi.