The BBC and BuzzFeed have obtained secret files that contain evidence of suspected match-fixing in tennis.
The investigation alleges that over the last decade a core group of 16 tennis players have repeatedly been brought to the attention of the sport's governing bodies over suspicions they have fixed matches.
The report claims all of the 16 players have ranked in the world's top 50 at some point and that more than half of them were playing in the Australian Open first round, which started on Monday.
Novak Djokovic and Serena Williams led the defence of top-level tennis following the allegations.
Djokovic, who said he rejected an indirect offer of money to fix a match in 2006, said he was not aware of any match-fixing at the top of the sport.
"From my knowledge and information about match-fixing or anything similar, there is nothing happening on the top level, as far as I know," the world number one said.
"There's no real proof or evidence yet of any active players. As long as it's like that, it's just speculation. So I think we have to keep it that way."
Williams said she has also never seen any indication of malpractice on the women's tour.
"Not that I'm aware of," the American said. "When I'm playing, I can only answer for me, I play very hard, and every player I play seems to play hard."
It is that alleged the Tennis Integrity Unit, set up by a number of governing bodies including the International Tennis Federation and the ATP in 2008, has repeatedly failed to act on tip-offs primarily related to irregular betting patterns.
However, Chris Kermode, president of the ATP which governs the men's professional tour, said the sport's authorities "absolutely reject" the suggestion that evidence of match-fixing has been suppressed.
Kermode said: "The Tennis Integrity Unit and the tennis authorities absolutely reject any suggestion that evidence of match-fixing has been suppressed for any reason or isn't being thoroughly investigated.
"And while the BBC and BuzzFeed reports mainly refer to events from about 10 years ago, we will investigate any new information, and we always do."
Three players have been given life bans for match-fixing since the TIU was set up in 2008, among them the former world number 55 Daniel Kollerer, who was found guilty in 2011 of making invitations to other players to fix matches on five occasions.
And while Djokovic implied the extent of the problem may be exaggerated, he reiterated that he was once offered £110,000 to lose a first-round match in St Petersburg - a bribe which was turned down before it even reached him.
"I was not approached directly," the Serbian said.
"I was approached through people that were working with me at that time, that were with my team. Of course, we threw it away right away. It didn't even get to me - there was nothing out of it."
The BBC and BuzzFeed chose not to name any players as they say it is not possible to determine whether they were personally taking part in match-fixing.
Roger Federer believes offenders need to be identified before significant progress can be made.
"I would love to hear names," the Swiss said.
"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 so all over the place. It's nonsense to answer something that is pure speculation."
The TIU's director Nigel Willerton refused to confirm whether players competing at the Australian Open are currently under investigation.
Tennis is the latest sport to be marred by claims of corruption after football and athletics have both been recently embroiled in controversy.
FIFA president Sepp Blatter resigned and was banned for eight years after he was found to have made a "disloyal payment" to UEFA counterpart Michel Platini, while officials at the IAAF continue to come under scrutiny from the French police and the World Anti-Doping Agency over a conspiracy to cover up doping in athletics.
Federer added: "We need to make sure the integrity of the game is always maintained because without that, I always would say, why do you come and watch this match tonight or any match? Because you just don't know the outcome.
"As long as we don't know the outcome, the players, fans, it's going to be exciting. The moment that gets taken away, there's no point any more to be in the stadium."
Secretary of State for Culture, Media and Sport John Whittingdale told BBC Radio 4's Today show: "I hope that tennis will learn from the mistakes of others sports and investigate this very quickly and openly.
"In the past, allegations of this kind made, which have been against athletics, against football, have appeared to be swept under the carpet and that has done enormous damage."