John McEnroe has proposed a men v women contest to prove his claim that Serena Williams would be ranked "700 in the world" on the men's circuit.
The seven-time Grand Slam champion said Williams was "the best female player ever" but against men it would be an "entirely different story".
Williams, a 23-time Grand Slam champion, responded to McEnroe, asking him to "respect me and my privacy".
McEnroe, 58, said: "I've got a solution. Men and women play together."
"Then we don't have to guess," added the American. "I'm sure the men would be all for it.