John McEnroe: I could beat Serena Williams

His confident assertion - "I believe that I could still take her" - came on Wednesday's episode of Jimmy Kimmel Live, when he revealed that presidential candidate Donald Trump had once asked the pair to face off against each other.

McEnroe, now 56, said that he felt Trump was "humouring" them both, and said they had "a lot to lose".

"Serena - she's got a lot to lose by losing to an old fart like myself," admitted McEnroe. "And I got a lot to lose, because if I lose to, God forbid, a woman, then I'm not allowed in any men's locker room for the next 15 years, or possibly the end of my life."

He revealed, however, that not all the McEnroes were so confident that he could beat the women's world number one.

"My daughters are over there [in the studio]," he said. "They think I'd probably lose to Serena."

Williams takes on Italy's Karin Knapp in the Western and Southern Open tonight.