Australian Open chiefs said Thursday that their Covid measures were working after several players questioned the "optional" testing policy at the Grand Slam.

Frenchman Ugo Humbert became the first known infection of a player at the tournament after he said Wednesday that he tested positive on his exit test to leave Australia following his first-round defeat.

Men's third seed Alexander Zverev said in response that players were not getting tested, even as infection numbers surge in Australia, and believes that "quite a few players" are infected, without providing evidence.

His remarks threw another spotlight on Covid policies at the Australian Open, which were already under scrutiny following the saga of deported defending champion Novak Djokovic.

Official attendees at Melbourne Park, such as tournament staff, are provided with rapid antigen tests each day and must be negative to remain on site.

Players are given kits too but it is only mandatory to test if they have symptoms and it is up to them to declare if they are positive.

Tournament director Craig Tiley defended the protocols, which saw all players having PCR tests on arrival in Australia and again between days five and seven.

"So far it's worked well and it's been successful," he told tournament host broadcaster Channel Nine.

Germany's Alexander Zverev believes there are players with Covid at the Grand Slam
Germany's Alexander Zverev believes there are players with Covid at the Grand Slam AFP / Martin KEEP

"We're in a position where this is day four and we're going to go into another 10 days of some great tennis.

"We're continuing with not only that testing programme but also the physical distancing and the wearing of masks -- you can see in the player area all the players have masks on."

Women's third seed Garbine Muguruza called testing for players an "optional thing".

"Me, I test every two days by myself in my room. It's not mandatory. I still do it," she said.

Asked if players had to show test results when they arrived at Melbourne Park, the Spaniard added: "No, don't have to."

Several players, including veteran Andy Murray, said they had also been testing themselves regularly.

"Ultimately the responsibility is upon the players to be testing themselves. And some will do that and some won't unfortunately."

Players at the Australian Open have to be vaccinated or have a medical exemption -- a rule central to the deportation of the unvaccinated Djokovic.