Gazzetta Dello Sport revealed that the sentence relates to the group sexual assault of a 22-year-old woman from Albania which was carried out by the Brazilian soccer star and five other men on January 22, 2013.
Robinho was playing for the Rossoneri at the time.
A Milan tribunal handed down the sentence to the 33-year-old, who is now playing for Atletico Mineiro.
Robinho is now in Brazil playing for Atletico Mineiro.
Robinho joined City from Real Madrid for £32.5m and would go on to make 53 appearances, scoring 16 times during his spell at the City of Manchester Stadium.
On the final day of the 2008 summer transfer window, City's wealthy new owners showed their intent by breaking the British transfer record to lure him from Real Madrid for £32million.
The attacker did go on to win the Serie A title with the Italian side, teaming up with Zlatan Ibrahimovic and Antonio Cassano to conquer the division.
The Brazilian now plies his trade with Atletico Mineiro in Brazil.