Monza chief Adriano Galliani has welcomed Balotelli with a warning: this is your last chance.
Monza are owned by ex-Milan President Silvio Berlusconi, with coach Cristian Brocchi and players including Kevin-Prince Boateng.
“I gave him a proper talking to, and told him this is truly the last, absolutely last, completely the last chance," Galliani told La Gazzetta dello Sport.
“I do love Mario, he's a player with the kind of technical and physical qualities that should've allowed him do so much more with his career.
“There were flashes of exceptional quality and I can't understand why he can't get even better. After all, he is only 30 years old."
The contract is short-term, until June 30, 2021, once Balotelli has passed his medical.