Maria Sharapova is the last remaining former women's champion at the Australian Tennis Open after Venus Williams retired injured early in her third round match in Melbourne.
Williams lasted only one game against 30th-seed Andrea Petkovic of Germany before pulling out on Friday.
She screamed in pain and stopped playing while receiving at 0-1 down.
AFP reports Williams limped to her chair and conceded defeat after seeing a trainer.
She earlier strained a muscle during her second-round match against Czech Sandra Zahlavova on Wednesday.
"I just obviously couldn't play," she said. "I mean, just couldn't move."
Defending champion Serena Williams missed the tournament through injury.
Justine Henin was beaten by Svetlana Kuznetsova 6-4 7-6(8) of Russia.
"She was just better than me, especially in the important moments," said Henin.
Sharapova, who is seeded 14th, beat Julia Goerges of Germany 4-6 6-4 6-4 to advance to the fourth round.
Women's world number one Caroline Wozniacki, 20, of Denmark, moved into the fourth round with a 6-4 6-3 win over Dominika Cibulkova of Slovakia. Wozniacki has not yet won a grand slam title.