Williams is facing fresh questions over her future in tennis after her much-hyped comeback ended with a first round defeat at Wimbledon
At her first Wimbledon, Harmony Tan defeated 23-time grand slam winner Serena Williams in the opening round on Tuesday.
Williams was beaten in her first singles match for a year but did not rule out coming back to Wimbledon.
The US Open champion takes on Caroline Garcia in round two on Wednesday.