The Brazilian defender, unwanted by Manuel Pellegrini, leaves the Etihad Stadium after less than a year at the club and returns to Italy with Rudi Garcia's side
The Serie A side tweeted a picture of the defender training with the club, alongside the message: "Welcome aboard, Maicon!"
The 31-year-old joined City from Inter in August 2012 for a fee of around €3.5 million and made his debut in a 1-1 draw away to Stoke City.
However, he struggled with injury throughout the season and only made 11 appearances in all competitions for the Blues.
New Manchester City boss Manuel Pellegrini revealed that he had no plans to include the right-back in the upcoming season and reports in Italy suggest that City paid the Brazilian €2m to get him to leave.
Maicon established himself as one of the world's leading defenders during his time at Inter, where he scored 16 goals in 176 league appearances.