Serena Williams says she is "super confident" a right shoulder problem will be fine for the Australian Open.

Williams will be bidding for a record-equalling 24th Grand Slam title when the tournament begins on Monday.

"I feel pretty good. I've gotten a lot of treatment already on my shoulder," the 39-year-old said.

US Open champion Naomi Osaka, one of the favourites for the Melbourne title, and Victoria Azarenka also withdrew from their warm-up events with injuries.

Japan's Osaka was set to face Belgium's Elise Mertens in the Gippsland Trophy semi-finals on Saturday but withdrew, citing a long-standing shoulder problem of her own.

"It kind of flared up again because I played a lot of matches back-to-back," Osaka said.

"My main focus is hoping I can rest enough before the Open."

Azarenka, who lost to Osaka in the New York final, pulled out of her Grampians Trophy quarter-final with a lower back injury.

There are six WTA and ATP events running at Melbourne Park to allow players to prepare after their mandatory quarantine in Australia.

Belarussian Azarenka has played just one match after spending 14 days in her hotel room following positive coronavirus tests on her flight into the country.

As the third seed, she received a first-round bye, before Thursday's play was cancelled when a hotel worker tested positive for the virus.

Defending champion Sofia Kenin, who was left in tears after her defeat by Garbine Muguruza in the Yarra Valley Classic last eight, said being unable to practise properly had impacted on her.

"After two matches, my leg is completely sore," the American said.

"You can see that being in a room for two weeks, not playing, practising, it's not the same as playing a match clearly.

"Today it is better and I want it to be better for the Open."

In the matches that did take place, Muguruza secured a meeting with Barty after thrashing Marketa Vondrousova 6-1 6-0.

The Spaniard has lost only 10 games in her five matches in Australia, but she has a 3-1 losing record against home favourite Barty.

In the Gippsland Trophy, Belgium's Mertens will play Kaia Kanepi, who overcame Ekaterina Alexandrova 6-3 7-6 (7-8).