Twenty-eight professional tennis players are being investigated over alleged match-fixing, Spanish police have revealed.
Although none of the players have been named, it is understood one of them competed in last year's US Open.
Cash in excess of £150,000 and a shotgun were among the items retrieved in a series of raids, following which 15 people - including some of the players - were arrested.
European Union law enforcement agency Europol, which supported the operation led by Spanish authorities, said at least 97 matches from lower-tier Futures and Challenger tournaments were fixed.
Europol said the investigation began in 2017 after the Tennis Integrity Unit (TIU) detected a number of irregular betting patterns in matches. Neither the TIU nor officials at the International Tennis Federation were immediately available for comment.
In a statement Europol said: "The suspects bribed professional players to guarantee predetermined results and used the identities of thousands of citizens to bet on the pre-arranged games.
"A criminal group of Armenian individuals used a professional tennis player, who acted as the link between the gang and the rest of the criminal group.
"Once they bribed the players, the Armenian network members attended the matches to ensure that the tennis players complied with what was previously agreed, and gave orders to other members of the group to go ahead with the bets placed at national and international level."