Reigning women's US Open champion Aryna Sabalenka advanced to the semi-finals on Tuesday when Marketa Vondrousova pulled out of their last-eight clash with a knee injury.

"I am sorry to announce that I have to withdraw from my quarter-final match this evening due to a knee injury," Vondrousova said in a statement.

"I tried my best to take the court today but during the warm-up I felt again my knee and after consultation with the tournament doctor decided not to risk aggravating the injury," she added.

World number one Sabalenka plays fourth-seeded American Jessica Pegula in the last four Thursday in a repeat of last year's final won by the Belarusian.

"So sorry for Marketa after all she's been through. She has been playing amazing tennis and I know how badly this must hurt for her," Sabalenka wrote on social media.

The 26-year-old Vondrousova had reached her second US Open quarter-final after knocking out two top-10 players in New York.

She took down seventh seed Jasmine Paolini in the third round and defeated Elena Rybakina in the last 16 in a battle of former Wimbledon champions.

But injury struck the unfortunate Vondrousova once again. Footage of Tuesday's practice session aired by ESPN showed Vondrousova doubled over and being consoled by members of her coaching team.

Vondrousova missed last year's US Open after undergoing shoulder surgery on the eve of the tournament. She also sat out the Australian Open in January.

The Czech returned briefly in February but then did not play again for three months before the French Open. (AFP)