Cassano made his debut for Milan in a friendly against Al-Ahli during the club's annual winter training camp in Dubai.
Milan won 2-1 thanks to goals from Clarence Seedorf and Giacomo Beretta.
“I didn't expect anything more [from Cassano],” Allegri said. “If one doesn't play for 20 days, you lose match rhythm, so you can imagine how it might be if one trains alone for two months.
“Training alone counts for little. But Antonio is now giving a lot. He has the right head on his shoulders.
“I am happy with what I have seen here in training camp.”