The transfer fee, salary and period were not disclosed.
The Brazilian player joined MU during 2008-10 when he was 19 years old. However, at the age of 28, he went on loan to Braga of Portugal for the first half of the 2009-10 season.
After leaving MU, Possebon played for Vicenza Calcio of Italy, Criciúma Esporte and Juventude of Brazil.
Alongside his teammates, Possebon won the U20 Brazilian Championship in 2006, FA Community Shield in 2008, Football League Cup in 2008-09, Campeonato Paulista and Copa Libertadores in 2011.
Possebon is expected to help HCM City shine at the National Premier League after their third-from-bottom finish in the 14-team V.League 1 last year.
Earlier, HCM City signed a two-year contract with former Vietnam national team coach Toshiya Miura and inked contracts with six other local players and one foreigner.
The 54-year-old Japanese coach was the manager of both the national and U23 squads of Vietnam in 2014-16.