NOVAK Djokovic and Serena Williams led the defence of top-level tennis following allegations of match-fixing over the last decade which is said to implicate a number of winners of grand slam titles.

An investigation carried out by the BBC and Buzzfeed alleges that over the last decade a core group of 16 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 yesterday.

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.”

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 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.

“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.

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 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.”

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.

UK 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.”