If John McEnroe reconsiders and accepts Donald Trump's million dollar offer to play Serena or Venus Williams ... one major celebrity has already picked the women to win.
"Man, Serena and Venus all the way," Common told us.
Of course, Common's a little biased ... he used to date Serena back in the day -- but maybe that's why he's confident Johnny Mac would take the "L" if they really throw down on the court.
As we previously reported, McEnroe says Trump made a real effort to make the $1 Mil Battle of the Sexes match a reality ... but John says he had no real desire to compete against a female.
... or maybe he's just scared.