Serena Williams continues to keep herself busy during her post-playing days ... the tennis GOAT is joining the Toronto Tempo ownership group ahead of the new WNBA franchise's inaugural season!
The Tempo made the announcement Monday morning, posting video to social media showing Williams bouncing a tennis ball ... which ultimately turns into a WNBA ball, with the text "New Court, New Game."

NEW BEGINNINGS @TempoBasketball
The new org also issued a press release .