US tennis legend John McEnroe expressed his concern on Friday that organised crime, such as the Russian mafia, could be infiltrating tennis.
The former world number one believes that threats to tennis players or their families could be forcing them into throwing matches.
"The thing that worries me is that mafia types, like the Russian mafia, could be involved. That's potentially pretty dark and scary," McEnroe told The Daily Telegraph.
"I think that's the side that people aren't really looking at with these match-fixing stories. Someone may have threatened the players, and they are put in a situation. I'm guessing that could happen. That would make more sense to me than top players throwing a match for money.
"Throwing a match for money would be stupid, as you would be risking losing what you've worked for your whole life. It seems crazy that players would take that risk for money. It would make more sense that they've been threatened in some way and that's why they're doing it."
Russian Nikolay Davydenko, the world number four, is being investigated by the ATP after a defeat in Poland in August while Italian Alessio di Mauro was suspended for nine months for betting on matches and Philipp Kohlschreiber has had to defend himself of accusations of match-fixing in the German press.
"With a high-ranked guy like Davydenko, he's making so much money to begin with that he'd be risking so much by doing it, as if you get caught you should be banned for life," McEnroe said.
"But it's pretty tough to prove that someone has thrown a match unless you're tapping the guy's phone or something."
But some of the lower-ranked players in men's tennis could be tempted by bribe money, McEnroe said.
"I think this issue has to be closely looked at, because it's very conceivable that it's happening. There are guys out there who are 100 in the world, 200 in the world, and they're making 50,000 pounds a year.
"And if someone says that they'll give you 50,000 pounds, so your entire year's money, I think there's a strong possibility that they have taken the money, without a doubt," McEnroe said.
"There is definitely temptation for people. It's becoming more of a drama because there's more money in sports."