He played there for 5 seasons and joined AEK Athens in 1956 with a two-year ban, as it was applied at the time when a player was transferred, without the approval of his club.

Papapostolou was a key player of the club in winning the championship in 1963,[2] while he also won the Cup in the following season.

He also worked in clubs of smaller categories, such as Atromitos, Marko, Ierapoli, Korinthos, Acharnaikos, Koropi, Panelefsiniakos and until December 1979.

In February 1980 he replaced Hermann Stessl on the AEK Athens,[5] where they finished in the 4th place, left out of the European competitions of the next season.

[10] Papapostolou was for a number of years the president of the Greek Football Coaches Association, with important reforms for the industry.