Serena Williams has withdrawn from the Australian Open ... saying she's not quite ready to compete on a tournament level after recently giving birth.
Serena posted the message to her Snapchat Thursday, saying ... "After performing in my first match after giving birth I realized that although I am super close I'm not where I personally want to be."
She adds ... "My coach and team always said 'Only go to tournaments when you are prepared to go all the way.'" Serena defeated her sister, Venus, in the Australian Open last year.
The new mom competed in a tennis match just last month -- her first since giving birth to a baby girl in September. It was an exhibition match against Latvian player Jelena Ostapenko at the Mubadala World Tennis Championship in Abu Dhabi.
As for the Australian Open ... she says she looks forward to coming back and competing another time.