Novak Djokovic, the top-ranked player in men's tennis, said Monday that a member of his support team was offered $200,000 to have Djokovic throw a match at a 2007 tournament in Russia.

Djokovic described the approach after the BBC and Buzzfeed News published reports that tennis authorities have suppressed evidence of match-fixing and overlooked suspected cases involving players ranked in the top 50, including Grand Slam singles and doubles winners.

The reports said that none of these players had faced sanctions and more than half would be playing at this year's Australian Open, which started Monday. The players weren't identified by name.

"I was not approached directly. I was approached through people that were working with me at that time," Djokovic said of the 2007 incident. "Of course, we (rejected) it right away. It didn't even get to me — the guy that was trying to talk to me, he didn't even get to me directly. There was nothing out of it."

Djokovic said he doubted corruption extended to the top level of the sport, and pointed to the enhanced monitoring systems put in place.

"We have, I think, a sport (that has) evolved and upgraded our programs and authorities to deal with these particular cases," he said. "There's no real proof or evidence yet of any active players (being involved in match-fixing), for that matter. As long as it's like that, it's just speculation."

The BBC and BuzzFeed allegations were based on files they reported had been leaked "from inside the sport" showing evidence of suspected match-fixing orchestrated by gambling syndicates in Russia and Italy that had been uncovered during an ATP investigation of a 2007 match in Sopot, Poland, involving suspiciously high levels of betting.

According to the reports, the ATP investigation widened to uncover a network of other players suspected of match-fixing, but officials didn't follow up on the cases. Since then, the reports said, the ATP has repeatedly been warned by bookmakers, foreign police and other investigators about many of the same players, but hasn't taken any action against them.

ATP chairman Chris Kermode maintained that the organization's Tennis Integrity Unit, formed in 2008, investigates every report it receives and takes action only when it has enough evidence to do so. It has since sanctioned 18 people for match-fixing, including five players and one official who received lifetime bans.

"You can have lots of information, lots of anecdotal reports, but it's about getting evidence that we can use," Kermode said.

Many of those punished have been lower-ranked players on the second-tier Challenger tour. Two of the most higher-profile players — former top-50 players Daniele Bracciali and Potito Starace — were initially banned for life before their suspensions were lifted by the Italian Tennis Federation last year.

"I would love to hear names," 17-time Grand Slam singles champion Roger Federer said after beating Nikoloz Basilashvili of Georgia 6-2, 6-1, 6-2 in his first-round match. "Then at least it's concrete stuff and you can actually debate about it. Was it the player? Was it the support team? Who was it? Was it before? Was it a doubles player, a singles player? Which Slam?"

"It's super serious and it's super important to maintain the integrity of our sport," Federer added. "So how high up does it go? The higher it goes, the more surprised I would be."

Other questions were raised Monday about whether the sport was sending mixed messages by allowing the bookmaker William Hill to become one of the Australian Open's sponsors this year and advertise on stadium courts.

''Honestly it's on a borderline, I would say," Djokovic said. "Whether you want to have betting companies involved in the big tournaments in our sport or not, it's hard to say what's right and what's wrong."