On Wednesday, Frenchman Ugo Humbert tested positive for Covid-19 in a pre-departure test following his first-round defeat against compatriot Richard Gasquet.
“Quite a few players had it when they arrived, quite a few players I think have it now,” Zverev told reporters after his second-round victory against John Millman.
“We are not getting tested, so I think if we would get tested, there would be probably more positives than there are now, in a way.”
All players must be fully vaccinated in order to play at the Australian Open, unless they have a valid medical exemption.
In an interview with Nine Network on Thursday, head of Tennis Australia Craig Tiley said that players had to test once they arrived in Australia and again between five and seven days after their arrival.
He added that tests are mandatory if a player has symptoms of Covid-19.
CNN has contacted Tennis Australia regarding its testing protocols at the Australian Open but has not received a response.
Garbiñe Muguruza, the third seed in the women’s draw, said after her second-round defeat against Alize Cornet that she had been testing every two days by herself in her hotel room, while Zverev also said that he had been taking extra precautions.
“There’s a lot of cases in Melbourne, there’s a lot of cases in Australia all around, so I don’t do much outside. I haven’t been to any restaurants yet, I haven’t been out, I haven’t been anywhere but the hotel room and the courts,” he said.
“I’m kind of doing a bubble for myself simply because I don’t want to take any risks and I want to give myself the best chance possible to do well here. If I get Covid then that’s obviously not going to happen.”
According to Victoria’s Chief Health Officer Brett Sutton, the state recorded 21,966 new cases of Covid-19 on Wednesday, giving a total of 246,894 active cases.
The Australian Open is set to conclude on January 31.