"Maybe at some point, a woman can be better than anybody", he said. But when asked whether she was the sport's best ever, regardless of gender, he made clear he didn't think so.
In fact, the 58-year-old went on to add she'd probably be 700th in the world!
"Maybe I should get her now because she's pregnant, but the truth is that I think that sometimes -I don't know why in tennis, I get it's that one battle of the sexes when Bobby Riggs played Billie Jean".
McEnroe may have realized what he said during the interview, as he granted that Williams has a mental toughness some male tennis players lack, but he still doubled down on his words.
Serena Williams has responded to John McEnroe's comments on NPR.
'And on a given day Serena could beat some players. "The reality of what would happen on a given day is Serena could beat some players, I believe, because she is so incredibly strong mentally".
"The men are a lot faster and they serve harder, they hit harder, it's just a different game". "I think it's mixed". She added, "I only want to play girls, because I don't want to be embarrassed".
Williams is taking a break from the tennis tour because she is pregnant.
It's important to note before we delve into this that McEnroe has his own conversational style and sensibility that doesn't translate well in text.
To be fair with John McEnroe, it may have been an honest assessment with regards to the differences between the physical attributes of men and women.
When the Williams Sisters were in the early stages of their career, they challenged any male tennis player outside the Top 200 in the rankings to an exhibition match. We had three kids together and my head was all over the place and I couldn't even think about. the transition that I was anticipating I was going to be making.
When rating the greatness of a woman athlete, why do we feel compelled to pull her out of her arena of competition and see how she would fare against men?
While McEnroe and Williams have never played, President Donald Trump approached McEnroe 17 years ago about playing a $US1 million, winner-take-all match against Venus or Serena Williams at his Trump Taj Mahal Casino in Atlantic City.
But then again, there's the physical difference between men and women.
Williams really wasn't having it.