LONDON (AP) — Serena Williams withdrew from her doubles match with sister Venus at Wimbledon on Saturday due to a right knee injury.

The 44-year-old Serena was injured during her singles return earlier in the week — in a three-set loss.

“I’m heartbroken to have to withdraw from doubles. Coming back to compete again has been a gift, and the opportunity to play alongside (at)venuswilliams once more meant the world to me. I did everything I could but unfortunately my knee just isn’t ready to compete,” Serena said in an Instagram post.

The post included images of four syringes that Serena said “shows the fluid they drained from my knee after my singles match.” An accompanying video showed her walking with strapping up and down her right leg and what appeared to be one of her daughters holding a cane for her.

However, with the U.S. Open approaching, Serena indicated she could play again somewhere else soon.

“All I can say,” Serena said, “is stay tuned to a city near you.”

The Williams sisters — Venus is 46 — were scheduled to play Camila Osorio and Solana Sierra. It was the only first-round doubles match that wasn't scheduled earlier in the week, having been pushed back to give Serena more time to recover.

Serena was beaten 6-3, 6-7 (6), 6-3 by 20-year-old Maya Joint of Australia on Tuesday.

Venus played in the mixed doubles tournament on Friday together with Kevin Krawietz, losing in straight sets to Tereza Mihalikova and Lloyd Glasspool.

The Williams sisters are six-time champions as partners in women's doubles at Wimbledon.

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AP tennis: https://apnews.com/hub/tennis