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.

Roger Federer was also asked about the emerging story - and admitted that he is worried. "You have to take it super serious," he said.

"This is more a question for guys in suits, not one in a tracksuit... I'd love to hear names."

“From my knowledge and information about, you know, the match fixing or anything similar, there is nothing happening on the top level, as far as I know. Challenger level, those tournaments, maybe, maybe not,” said Federer.

“But I'm not entitled to really talk about it. I can give my opinion. But there is an organization, authorities, people who take care of that on a daily basis and make sure to track it down."