Serena Williams withdrew from the women’s doubles event at Wimbledon because of a right knee injury, ending her planned reunion with sister Venus Williams at the tournament.The 44-year-old suffered the injury during her return to singles earlier this week, where she lost a three-set match.Announcing her withdrawal in an Instagram post, Serena wrote: “I’m heartbroken to have to withdraw from doubles. Coming back to compete again has been a gift, and the opportunity to play alongside Venus Williams once more meant the world to me. I did everything I could but unfortunately my knee just isn’t ready to compete.”Along with the post, Serena shared pictures of four syringes, saying they showed “the fluid they drained from my knee after my singles match.” She also posted a video of herself walking with heavy strapping on her right leg, while one of her daughters appeared to be carrying a cane for her.Despite the setback, Serena suggested she could return to competition before long, with the US Open approaching.“All I can say,” Serena added, “is stay tuned to a city near you.”The Williams sisters had been scheduled to face Camila Osorio and Solana Sierra in the first round. Their match was the only women’s doubles first-round contest not played earlier in the week, after it was delayed to give Serena more time to recover.Serena had returned to singles action on Tuesday but was beaten 6-3, 6-7 (6), 6-3 by Australia’s 20-year-old Maya Joint.Venus also featured in the mixed doubles event on Friday alongside Kevin Krawietz. The pair lost in straight sets to Tereza Mihalikova and Lloyd Glasspool.The Williams sisters have won six Wimbledon women’s doubles titles together.