Novak Djokovic is facing a race to be fit for his last-16 match against Milos Raonic on a day of intriguing match-ups at the Australian Open on Sunday.
Grand Slam winners Garbine Muguruza, Naomi Osaka, Serena Williams, Dominic Thiem, Iga Swiatek and Simona Halep are also in behind-closed-doors action.
Djokovic suffered an abdominal injury during his third-round win over Taylor Fritz and did not practise on Saturday.
“I don’t know if I will step on court,” the Serb said after Friday’s victory.
The world number one has been given the maximum time to recover as his match against Raonic is the final one on Rod Laver Arena on Sunday.
Eight-time Australian Open champion Djokovic needed courtside treatment against Fritz and later said he thought he had torn a muscle, adding: “I don’t know if I will recover from that in two days.”
The top seed has a perfect record of 11 wins from 11 matches against 30-year-old Canadian Raonic, including three-set victories in the Australian Open quarter-finals in 2020 and 2015.
A great-looking day seven schedule
Five Grand Slam winners play on the same court in the women’s singles fourth round on a brilliant-looking schedule on Rod Laver Arena.
It begins at 00:00 GMT with Spain’s Muguruza, a winner at the French Open and Wimbledon, facing Japan’s Osaka, who has won the US Open twice and triumphed in the Australian Open in 2019.
“I don’t think we’ve played each other before,” said Muguruza, who has not dropped a set so far. “I am just happy with being in the second week of a Grand Slam. It shows my game is there.”
Williams, 39, is one Slam away from matching Margaret Court’s all-time record of 24 major singles titles and is second on Rod Laver Arena. She takes on 22-year-old Belarusian Aryna Sabalenka, with the seventh seed aiming to reach her first Grand Slam quarter-final.
All matches will be played without any fans in attendance until at least Thursday because of a snap five-day lockdown for the state of Victoria.
“It’s going to be a rough few days for I think everyone,” Williams said of the new restrictions. “But we’ll hopefully get through it.
“It’s not ideal. It’s been really fun to have the crowd back, especially here. It’s been really cool, but we have to do what’s best.
“I think basically we just go to the tennis, to the hotel. I’ve been doing that for 20 years, so I think I’ve been pretty much quarantining for my whole career.”
Poland’s Swiatek, 19, won the French Open in October and she meets Romanian second seed Halep, a beaten finalist in 2018 in Melbourne before she went on to clinch the French Open later that year and Wimbledon in 2019.
Auger-Aliassime aims to end Karatsev’s great run
US Open champion Thiem fought back from two sets down to win a five-set thriller against Australia’s Nick Kyrgios in front of 5,000 passionate fans on Friday, just before the lockdown began.
The third-seeded Austrian will face 2017 semi-finalist Grigor Dimitrov, the 18th seed from Bulgaria.
Alexander Zverev, the man Thiem beat in the final in New York in September, takes on Serbia’s Dusan Lajovic, with Canada’s Felix Auger-Aliassime aiming to end the brilliant run of qualifier Aslan Karatsev.
The Russian, ranked 114th in the world, had to get through three rounds of the qualifying tournament in Doha to get to Melbourne and knocked out Argentine eighth seed Diego Schwartzman in the previous round.
Tennis Breakfast will be on BBC Radio 5 Live Sports Extra from 07:00 GMT on Sunday, with live radio and text commentary of Swiatek v Halep and Djokovic v Raonic from 08:00 GMT.