The club founded in 1925 and ranked as the ninth most successful in world football with 75 national trophies are being investigated for a league fixture against Atromitos in February 2015.
The latest probe could see owner Evangelos Marinakis hit with a €2-million fine and a lifetime ban from football if the allegations are proven true.
Olympiacos won the match 2-1 and went on to win the title, while Atromitos qualified for the SuperLeague Greece playoffs.
Greek outlet SDNA has confirmed that the investigation has been reopened while other matches are also now being analysed.
The 39-time league champions recently knocked Arsenal out of the Europa League after scoring a late goal in a 2-1 win at the Emirates but could find themselves in the second-tier next season.