Spain's Civil Guard has revealed that 83 people have been implicated in the scandal, including 28 players from the ITF Futures and Challenger tours.
The police raided 11 houses and seized 5 luxury vehicles along with weapons, jewelry, electronic devices, credit cards, and Euro 167,000.
The arrests, which included one player who appeared at last year's US Open, follow an investigation into match-fixing by an organised Armenian criminal gang.
The Civil Guard said that the operation had been prompted by complaints from the Tennis Integrity Unit, the sport's anti-corruption body.
It did not identify those detained or being probed but said one of them played in the last US Open.
Fornell-Mestres was handed a provisional suspension from the sport at the end of a year ago following an investigation into what the TIU described as "alleged breaches of the Tennis Anti-Corruption Program".
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Authorities said the players tainted results after taking bribes from an Armenian ring that was dismantled in October. "They then gave the order for bets to be laid both nationally and internationally", added the statement.
"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".
According to the Civil Guard, which investigated the corruption along with Europol and Spanish tax authorities, the match-fixing group had been operating since at least February 2017, generating millions of dollars in profit.
They have frozen 42 bank accounts as part of the investigation into how the matches were fixed and the accompanying receipt of cash.
Professional tennis' anti-corruption body past year complained about irregular activities at games, including prearranged matches, at the lower-tier ITF Futures and Challenger tournaments.
"They would rig matches in order to place multiple and simultaneous bets on a national and worldwide level", the Civil Guard said in a statement.