Roger Federer called for 'concrete' facts while Novak Djokovic spoke of his team once being offered $200,000 to fix a match as the multiple grand slam champions reacted to claims of widespread match-rigging in tennis on Monday.

The opening day of the Australian Open was overshadowed by reports in the BBC and online BuzzFeed News accusing tennis authorities of failing to deal with 16 players repeatedly flagged up to the Tennis Integrity Unit (TIU) over suspicions of matches being thrown.

Both Federer and defending champion Djokovic strolled through their opening matches in Melbourne, but were inevitably asked about the story rocking the sport.

"I would like to hear the names," 34-year-old Federer told reporters when asked to comment on claims that grand slam champions were among the players involved and that eight of them were playing in the Australian Open.

"I would love to hear names. 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."

Federer, the most successful male player of all time with 17 majors, said it was "super serious" for the sport, but said he would be surprised if top players were involved.

"So how high up does it go? The higher it goes, the more surprised I would be, no doubt about it," he said.

"We've got to do everything keep the sport clean. It's vital, there's no doubt about it."

World number one Djokovic said he doubted whether match-rigging was taking place in the higher echelons of the game but said his team had been approached in 2007 to throw a match.

"I was approached through people working with me," he told reporters. "Of course, we threw it away right away. It didn't even get to me.

"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." – Reuters