Tim Ireland/Associated Press

Former tennis star and current commentator John McEnroe said on In Depth with Graham Bensinger that Donald Trump once offered him $1 million to play a match against Serena or Venus Williams.

"I was calling a match and suddenly I get this envelope, and it's from Donald Trump, who is promoter galore. ... So he wrote me a letter, it went, 'Dear John, I want to offer you $1 million to play either Serena or Venus."

McEnroe turned down the offer, saying he never had the desire to play a woman in a match, though he believed at the time that he could have beaten either woman, noting that he was once the No. 1 player in the world.

He added that he is less certain that he can beat either Williams sister in the present, however, and his daughters have their doubts.

"'Dad, I don't know if you can beat Serena,'" McEnroe said they told him. "I'm like, 'God. I can't even get my kids on my side.'"