The American tennis star said that Williams would rank 700 on the men's tour
American tennis legend John McEnroe says he won't apologise to Serena Williams after saying she'd rank about 700th on the men's tour.
The 23-time Grand Slam winner responded by saying she "adores" and "respects" McEnroe - but he should avoid saying things "not factually based".
In an interview with American broadcaster CBS, McEnroe said his comments "weren't necessary" but refused to offer an apology.
Asked by CBS This Morning co-host Norah O'Donnell if he wanted to apologise, he replied "no", instead saying that men and women should play together to end the debate.
"It seems in tennis, unlike in other sports, they ask about women and how I would do," he said. "How would John McEnroe do against Serena [Williams]?
"To solve the problem - I'm sure the men will be all for this - [we should] have men and women play together. And then we don't have to guess."
He went on to rank his top five of all time, in which he placed Serena Williams at number five, just ahead of Novak Djokovic.