Aryna Sabalenka was sad to see her would-be quarterfinal opponent bow out of the U.S. Open before their Tuesday match.

Markéta Vondroušová withdrew from the Grand Slam with a knee injury that she did not want to exacerbate further.

Sabalenka, the defending women’s singles champion, took to social media to pen an emotional note to Vondroušová.

“So sorry for Marketa after all she’s been through,” Sabalenka wrote on her Instagram Story after the news broke that their match at Arthur Ashe Stadium would not be taking place. “She has been playing amazing tennis and I know how badly this must hurt for her. Take care of yourself and I hope you can recover quickly. Love Aryna.”

The 26-year-old Vondroušová, the 2023 Wimbledon champ, came into the tournament unseeded and won three straight matches — losing just one set in a third-round win over No. 9 Elena Rybakina — to set up a battle with Sabalenka.

In a statement to the U.S. Open, Vondroušová explained that she consulted with the tournament’s doctor and decided not to push her knee issue further.

“I am sorry to announce that I have to withdraw from my quarterfinal match this evening due to a knee injury,” Vondroušová, who has battled multiple injuries the past few years, said. 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. I appreciate all the support this tournament and apologize to the fans who were looking forward to the match.

“I had an amazing time here in NY and can’t wait to be back next year.”

Sabalenka, the No. 1 seed, will face off with No. 4 Jessica Pegula on Thursday at Arthur Ashe in a rematch of last year’s U.S. Open final.