Retired tennis great John McEnroe said he is worried that the Russian mafia and other organized crime might have infiltrated professional tennis, AFP reported Friday.

"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.

McEnroe, a former No. 1 and part of the heyday of American tennis prior to the Sampras-Agassi era, said he believes players are throwing matches because of threats to themselves and their families.

"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."

McEnroe's comments come on the heels of suspicions regarding Russian player Nikolay Davydenko, the fourth-ranked player in the world. He is being investigated by tennis governing body ATP after a strange defeat in Poland in August.

Moreover, Alessio di Mauro of Italy was suspended for nine months for betting on matches and Philipp Kohlschreiber of Germany has denied accusations that he has fixed matches.

"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.

Mike Ehrmann / Getty Images The Week in Sports Pictures The nation grieved for those hurt, killed and affected by the Boston Marathon bombings. After one of the suspects was caught on Friday — following a day-long lockdown and manhunt — sports returned to Boston over the weekend.

"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."