Serena Williams pulled out of the women’s doubles event at Wimbledon due to a right knee injury, potentially reuniting with her sister Venus Williams in the tournament.The 44-year-old suffered an injury on his return to singles earlier this week, where he lost in three sets.Announcing her retirement in an Instagram post, Serena wrote: “I’m heartbroken to be giving up doubles. To be back competing again has been a gift, and the opportunity to play with Venus Williams once again meant the world to me. I did my best but unfortunately my knee wasn’t ready to compete.”Along with the post, Serena shared photos of four syringes, saying that they showed “the fluid they took out of my knee after my singles match.” He also posted a video showing him walking with heavy ropes on his right leg, while his daughter is seen carrying a cane for him.Despite the difficulties, Serena said she could return to competition soon, with the US Open approaching.“All I can say,” Serena added, “is I’m still living in a city near you.”The Williams sisters were scheduled to face Camila Osorio and Solana Sierra in the first round. Their match was the only women’s match not played earlier in the week, having been delayed to give Serena more time to recover.Serena returned to action on Tuesday but was beaten 6-3, 6-7 (6), 6-3 by 20-year-old Australian Maya Joint.Venus also appeared in a mixed doubles event on Friday alongside Kevin Krawietz. The duo lost in straight sets to Tereza Mihalikova and Lloyd Glasspool.The Williams sisters have won six Wimbledon singles titles together.