Serena Williams has withdrawn from her Yarra Valley Classic semi-final against world number one Ashleigh Barty with a right shoulder injury.
Williams had earlier beaten fellow American Danielle Collins 6-2 4-6 10-6 in the last eight in Melbourne.
Australian Barty, who won 7-5 2-6 10-4 against American Shelby Rogers, has received a walkover into the final.
Williams will be seeking a record-equalling 24th Grand Slam singles title at the Australian Open.
The first Slam of the year begins on Monday and all six ATP and WTA warm-up events are being held at Melbourne Park.
Williams, 39, won her last major title at the Australian Open in 2017. She missed the 2018 competition and reached the quarter-finals in 2019, but fell in the third round last year.
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Barty will play either Garbine Muguruza or Marketa Vondrousova in the final.
Spain's Muguruza thrashed Australian Open champion Sofia Kenin 6-2 6-2 in a rematch of last year's final.
The USA's Kenin made 28 unforced errors and left the court in tears after the 77-minute defeat.
Czech Vondrousova beat Nadia Podoroska of Argentina 3-6 6-3 10-4.
Third sets in the WTA are being played over a 10-point super tie-break following the delay to the tournaments because of Covid-19 testing.
Azarenka through but Halep out
Victoria Azarenka saved two match points in her first match of the year to beat Kazakhstan's Yulia Putintseva and reach the Grampians Trophy quarter-finals.
The Belarussian, who is a two-time Australian Open champion, overcame a dreadful second set to win 6-4 1-6 11-9.
She will play Estonia's Anett Kontaveit next after the sixth seed beat Bethanie Mattek-Sands 7-5 7-5.
Angelique Kerber, a former world number one and the 2016 champion at Melbourne Park, beat Ons Jabeur 6-4 6-4 to set up a quarter-final against Maria Sakkari.
However, top seed Simona Halep appeared to struggle with a lower back problem as she lost her Gippsland Trophy quarter-final.
Two-time Grand Slam champion Halep won the first two games of the match against Ekaterina Alexandrova before the Russian breezed past her 6-2 6-1.
Halep received medical attention after the first set and was given a lower back brace but her movement and power was lacking throughout the match.
Alexandrova will play Kaia Kanepi of Estonia in the semi-finals.
Japan's Naomi Osaka, who is one of the favourites for the Australian Open title, advanced with a 7-5 6-1 win over Irina-Camelia Begu of Romania.
She will play Elise Mertens after the Belgian edged out world number five Elina Svitolina.
Svitolina trailed Mertens 5-2 in the second set but mounted a comeback, saving three match points to force a super tie-break.
However, the Ukrainian was punished for a slow start in the decider, with Mertens coming through 6-3 5-7 10-6.
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