Novak Djokovic says match-fixing is not prevalent at the top level of tennis, as allegations of corruption overshadow the start of the Australian Open.
The world number one, who claims he rejected £110,000 to lose a match early in his career, says there is "no real proof" of fixing among the elite.
"It's just speculation," said the Serb 10-time Grand Slam champion.
The BBC and BuzzFeed News have obtained secret files that contain evidence of suspected match-fixing in tennis.
Those files indicate that, over the past decade, 16 players who have been ranked in the world's top 50 have been repeatedly flagged to the Tennis Integrity Unit (TIU) over suspicions they have thrown matches.
All of the players, including winners of Grand Slam titles, were allowed to continue competing.
Chris Kermode, head of the Association of Tennis Professionals, has rejected claims that evidence of match-fixing had "been suppressed for any reason or isn't being thoroughly investigated".
But he added: "While the BBC and BuzzFeed reports mainly refer to events from about 10 years ago, we will investigate any new information."
UK Government minister John Whittingdale has told the BBC that tennis should "learn from the mistakes of other sports" and take prompt action.
He said that "past allegations of this kind" against athletics and football were seemingly "swept under the carpet".
The Secretary of State for Culture, Media and Sport added: "These are serious allegations and they need to be looked into very quickly."
Prime Minister David Cameron said he is "deeply concerned" that another sport is facing accusations of corruption.
His official spokeswoman said that "fans suffer most" from this alleged wrongdoing and these issues need to be investigated.
According to the BBC and BuzzFeed News, tennis authorities were presented with an examination of 26,000 matches in 2007, three of them at Wimbledon, which contained enough evidence to root out offenders.
However, no action was taken.
Nigel Willerton, who heads the TIU, insisted there had been a rigorous examination of material.
"All credible information received by the TIU is analysed, assessed and investigated by highly experienced former law-enforcement investigators," he said.
Djokovic had already revealed he had been approached to lose a first-round match at the St Petersburg Open in 2007.
"I was approached through people working with me," he said. "Of course, we threw it away right away. It didn't even get to me."
He added: "From my knowledge and information about match-fixing, there is nothing happening at the top level, as far as I know.
"At challenger level, maybe, maybe not. But I'm not entitled to really talk about it. I can give my opinion.
"But there is an organisation, authorities, people who take care of that on a daily basis and make sure to track it down."
A number of players competing at the Australian Open in Melbourne have been responding to the revelations.
Like Djokovic, Roger Federer said it was difficult to gauge if and to what level fixing went on, adding he wanted more information about who might be guilty.
"I would love to hear names,'' said the former world number one. "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?''
The 17-time Grand Slam champion added: "It's super serious and it's super important to maintain the integrity of our sport.
"So how high up does it go? The higher it goes, the more surprised I would be."
World number one Serena Williams said that if match-fixing was taking place, then she "didn't know about it".
The American added: "When I'm playing, I can only answer for me. I play very hard, and every player I play seems to play hard."
Williams began the defence of her Australian Open title with a 6-4 7-5 win over Italy's Camila Giorgi.
Djokovic, who is the reigning men's champion, started with a 6-3 6-2 6-4 defeat of South Korea's Chung Hyeon.
The leaked files included details of an investigation into a 2007 match between Russian Nikolay Davydenko and Argentine Martin Vassallo Arguello.
Both players were cleared of violating any rules, but the investigation developed into a much wider inquiry looking into a web of gamblers linked to top-level players.
Documents show the inquiry found betting syndicates in Russia, northern Italy and Sicily making hundreds of thousands of pounds betting on matches investigators thought to be fixed.
In a confidential report for the tennis authorities, the enquiry team said 28 players involved in these matches should be investigated, but the findings were never followed up.
Kermode said the TIU had won 18 convictions, including six life bans, since it was set up in 2008, adding that it "has to find evidence as opposed to information, suspicion, or hearsay".