Cassano is already training with Milan as his move from Sampdoria is finalised.
Allegri said: "Cassano isn't a monster, he's a professional.
"He will find it easy to be part of an atmosphere of good manners and respect for the rules.
"Antonio has the fortune of being at Milan and he will give us a hand.
"He finds a group of players with moral and technical values. It's an unrepeatable chance for him, the last of his career. I don't judge people at least until after I've heard them speak. I make an effort to get to know them.
Asked to reveal how he intends to play Cassano, Allegri replied: "As a striker. But things change in football."