"I've never played anyone ranked 'there' nor do I have time. Respect me and my privacy as I'm trying to have a baby. Good day, sir."
McEnroe had added that he believed Williams "could beat some players" on a given day, "because she is so incredibly strong mentally".
"She could overcome some situations where players would choke because she's been in it so many times, so many situations at Wimbledon, the US Open, etc," he said in the interview with National Public Radio.
Williams in the past has said that "men's tennis and women's tennis are completely, almost, two separate sports".
"The men are a lot faster and they serve harder, they hit harder. It's just a different game. I love to play women's tennis. I only want to play girls, because I don't want to be embarrassed," she said four years ago.
Dmitry Tursunov, who is the 701st ranked player in the world said he believed he could beat Williams.
The Russian said that while he thought McEnroe was "trying to talk women's tennis down", he added that "the reality" was that "men are stronger in general".
"I would hope that I would win against Serena," he told the BBC. "I'm much better than my ranking would suggest. She is pregnant, and I'm not."
