The French league organization said on Wednesday that an "unusual amount of bets" had been placed on Wahi receiving a yellow card during a league match in May for Nice.
"The investigation concerns suspected crimes involving organized fraud, organized sports corruption, bribery and money laundering," said the Marseille prosecutor's office, adding that Wahi was arrested on May 29, questioned and then released.
Wahi has not commented on the suspicions that appeared to prevent him from Ivory Coast's second World Cup match after Canada denied him a visa. A source close to the player told AFP on Thursday that Wahi would be allowed to enter Canada despite that.
The 23-year-old Wahi came on loan to Nice from German side Eintracht Frankfurt in January and has scored nine goals in 18 matches.
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