As many as 23 players in the French professional leagues may have bet online against their own club.
The figure comes from a wider investigation by the Ligue de Football Professionnel (LFP) into a total of 87 players who have broken French law by betting on matches sanctioned by the LFP.
The perpetrators were found by crosschecking files held by the online betting regulators ARJEL and then comparing them with the names and details of 1,600 footballers.
LFP president Frederic Thiriez said that "no known or emblematic player" was to be investigated and that there is no suspicion of fraud or match- fixing.
The 87 players to be investigated reportedly include 19 players from Ligue 1, 54 from Ligue 2 and 14 from the third division.
The average amount gambled was just 20 euros, although 14 players bet more than 500 euros.
Professional football players have been barred from betting on LFP matches since 1 February 2012 and the law has been widely publicised to affected players.