Serena Williams pulled out of the China Open after after sustaining a knee injury.
After returning to play her first major tournament in 16 months, Serena Williams was forced to withdraw from the French Open before her fourth-round matchup due to a pectoral injury.
Serena Williams defeats her sister Venus in straight sets to win the Australian Open and her 23rd career Grand Slam title.
Venus and Serena Williams will face off against one another on Friday night in the third round of the U.S. Open.
Tennis legend Lindsay Davenport says pressure could affect Serena Williams' quest for a 23rd Grand Slam title.