John McEnroe has refused to apologise for comments he made about Serena Williams and said he did not expect his views on the 23-time grand slam champion to cause such a stir.

McEnroe hit the headlines following an NPR interview over the weekend when he said: "If [Williams] played the men's circuit she’d be like 700 in the world." 

His comments came after the host, Lulu Garcia-Navarro, said Williams could be seen as the "best player in the world" instead of the "best female player."

Reaction to what McEnroe said has been strong, but when given the chance to apologise Wednesday (AEST) on CBS This Morning, the legendary seven-time major champion did not back down.

Presented Norah O'Donnell asked if he would like to apologise to his fellow American and McEnroe replied: "No."

McEnroe added "She's the greatest female player that ever lived, then the lady said to me, I don't remember which one, but she said, 'why did you say woman, why don't you just say the greatest, you know, tennis player that ever lived?'

"And so then I felt the need, however unfortunately probably, to defend myself. I don't know, just say what I really felt, which is about what I think she would be."

McEnroe continued: "I don't want anything to go wrong with Serena because she's pregnant. I don't want to upset her or whatever it was. She's — I think she was doing a tongue-in-cheek as well. And I think that deep down we're talking about something — I can't even believe we're talking about it."

Williams responded to McEnroe's comments on Twitter.

"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."

Near the end of the interview, McEnroe mocked the situation by being asked to re-rank the world's top five tennis players ever, and ranked Williams fifth.