A place at next year's tournament will be secure if the Italians beat their opponents in Florence's Artemio Franchi stadium.
The road to Euro 2012 has been seemingly smooth for the Group C leaders, but the cracks could be completely covered if the faithful turn out in force as Prandelli asks for the 12th man to be ever present.
"I would be very happy if there are 15,000 fans at the Franchi, that is a lot," Prandelli told Rai Uno.
"But unfortunately a lot of people are only interested in the team during important matches. I want more warmth to be shown towards Italy from the fans.
"I want people to feel like they are wearing the Italy shirt."
Italy are eight points ahead of Slovenia heading into the game and they have a game in hand.
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