The 17-year-old was expected to lead Team USA's 12-person tennis team at the Tokyo Games, which begin in just a few days.
The 17-year-old American took out her frustrations on her racket during a quarterfinals defeat against Barbora Krejčíková.
The two tennis stars faced off again at the Australian Open after memorably sharing a tear-jerking moment at the U.S. Open last August.
The tennis stars are set to play each other in the third round of the Australian Open.
The 15-year-old made headlines when she defeated the tennis superstar in July.
"I couldn’t thank her enough,” the 15-year-old tennis prodigy said.