MELBOURNE: World number one Novak Djokovic said a member of his staff was approached about fixing a match early in his career, and he questioned whether betting companies should be allowed to sponsor big tennis tournaments.

The reigning Australian Open champion was speaking after the sport was rocked by allegations that the authorities had failed to deal with widespread match-fixing.

Djokovic said that as far as he was aware there was no longer a problem with what he described as a "crime in sport" at the top level of tennis, but added that he had once been approached indirectly to throw a match.

"I was not approached directly, I was approached through people that were with my team," he said, after cruising through his opening match at the tournament against South Korean teenager Chung Hyeon on Monday.

"Of course, we threw it away right away. The guy that was trying to talk to me, he didn't even get to me directly. There was nothing out of it.

"Unfortunately, there were some, in those times, those days, rumours, some talk, some people were going around. They were dealt with. In the last six, seven years, I haven't heard anything similar."

In 2007, Djokovic said an approach had been made offering him $200,000 to throw a match at the St Petersburg Open in Russia, a tournament he did not ultimately play in.

The 28-year-old Serb said that although he was confident there was no longer a problem at the top level, he could not speak for further down the tennis rankings.

Djokovic was also asked about the propriety of betting companies being sponsors of major tennis tournaments, even if there had never been allegations that such companies were involved in any wrongdoing.

William Hill became the first "official wagering partner" of the Australian Open last year, and this year advertisements for the British bookmaker adorned the three main showcourts at Melbourne Park for the first time.

Critics, who say the relationship sends out the wrong message, have called on Tennis Australia to end it, and Djokovic said there should at least be a debate.

"Well, this is a subject for discussion, I think, today and in the future. It's a fine line. Honestly it's on a borderline, I would say," he 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.

"One of the reasons why tennis is a popular and clean sport is because it has always valued its integrity," he added.

William Hill defended its association with Tennis Australia.

"Close partnerships between regulated and licensed betting operators like William Hill and sporting bodies are part of the solution to integrity issues, not part of the problem," said group director of security, Bill South, in a statement.

"We have comprehensive information sharing agreements to inform the sport's integrity bodies and for the sport to promote licensed operators is key to ensuring transparency," he added.

Tennis Australia did not have an immediate comment to make.