No, he's not hurt. He didn't get kicked out of the squad. In fact, it's likely that Maggio will be watching the match from home, buried underneath a giant pile of blankets, with a hot cup of tea and a bowl of soup on standby.
He's sick, you see.
Maggio has apparently been felled by the flu, leaving him in no shape to head to Genoa to train with the Italy squad, much less play in tomorrow's match. Even if it weren't pouring buckets around the area like it is right now, Maggio's much better off staying at home and recuperating.
It's likely that this is the same flu that knocked down Marek Hamsik recently, keeping him out of a Europa League match and clearly hampering him against Fiorentina earlier this month. It's likely that a few other Napoli players have been ill as well, but thanks to the international break not causing them to miss anything important it hasn't come up.
Hopefully Maggio and whoever else is under the weather recover quickly. Being sick is no fun at all. Missing important events because of it is even less so. Hopefully Maggio will be able to earn more callups in the future, though at his age that's far from a guarantee.