He continued, explaining to NPR that he felt Williams was an “incredible player” and how, “[O]n a given day, Serena could beat some players. I believe because she's so incredibly strong mentally that she could overcome some situations where players would choke 'cause she's been in it so many times, so many situations at Wimbledon, The U.S. Open, etc. But if she had to just play the circuit — the men's circuit — that would be an entirely different story."