"It didn't go over big with my daughters," McEnroe admitted, before explaining the questioning that led to his much-criticized statement.
"We were talking to someone on NPR radio and she said something to the effect, she was asking about Serena, and I said, 'Serena Williams is the greatest female tennis player that ever lived and I think she's absolutely tremendous,'" he recalled. "She followed up with, 'Why do you have to say female tennis player? Isn't she the greatest tennis player that ever lived?' And I just said, 'Well wait, whoa, whoa, whoa, hang on a second here. If we're going to talk about that, you get into a little different category.'"
"Do they say that about girl basketball players, that they're as good as Michael Jordan, for example?" McEnroe tried to argue.
"People always ask me, 'Can you beat Serena Williams?'" he said. "My girls don't think I could beat her now. I thought I could beat her. She's pregnant, so maybe I should play her now. I'd have a better chance.
"But either way, I wish her the absolute best," he continued. "She's the best thing that's happened to American tennis in the last 10 to 15 years."
Williams, who is currently expecting her first child with fiance Alexis Ohanian, clapped back at McEnroe's statements on Monday, asking him to keep her out of his claims "that are not factually based."
"Dear John, I adore and respect you but please please keep me out of your statements that are not factually based," she wrote. "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."
Earlier this month, Williams shared a video of herself killing it on the court, baby bump and all. See more in the video below.