The Italian media have been speculating about what mysterious illness the player is suffering from, with Italian news agency ANSA claiming that the boy from Bari was struck by a type of stroke.
Milan, though, quickly issued a statement in response to the claims being made about the Italian international.
"Milan communicates that the information in circulation containing hypothetical diagnosis on the health of Antonio Cassano cannot be considered as verified," a media release read.
"They were not ascertained from medical sources such as the club's medical staff or from the doctors at the Policlinico of Milan who are treating the player.
"Milan also underline that Cassano is clearly improving and he will have further tests in the coming days."