Cassano is reportedly not happy with Milan's transfer strategy this summer, after the Italian outfit were forced to sell key players Zlatan Ibrahimovic and Thiago Silva to Paris Saint-Germain for financial reasons.
A number of veterans, including Clarence Seedorf, Gennaro Gattuso and Alessandro Nesta, also left in the summer, reportedly leading Cassano to question the Rossoneri's ambitions this season.
However, Allegri hopes that the 30-year-old remains committed to Milan.
"Antonio is a Milan player and can do well here," he said. "There are 15 days left to the transfer deadline and we'll see what happens. He is our player, so has to be a professional and work to give his best.
"I wanted to speak to Cassano to understand the situation, confirming to him that he is an important player who is technically gifted. I wanted him to give me the all-clear that he's staying here voluntarily and is convinced of our project.
"We did great things for him – we helped him heal from his heart surgery, got him back to fitness and ready to play at Euro 2012. We showed all our interest in keeping him here with us."
Cassano joined Milan from Sampdoria in January 2011.