Cassano left the former Italian champions for Inter Milan last week, claiming that Galliani had backed down on his promise to give him a new and improved contract.
"Cassano? It's the first time that such a thing has happened to me, and I also hope that it's the last time," Galliani told Sky Sport Italia.
"I will only say that if I had made a promise, then I would have kept it.
"I have never made any promises when it comes to extending contracts, especially not if we were in 2011 and then to extend a contract that doesn't expire until 2014. I wouldn't do that."
Cassano made his debut for Inter on Sunday in their 3-0 away victory over Pescara in Serie A.