John McEnroe has kept a close eye on the women's game since retiring, helped by his role as a commentator.
The former world number one regularly works at tournaments, staying involved with the sport he once dominated.
McEnroe won seven Grand Slam singles titles during his playing days and spent time at the top of the rankings.
When asked to pick his Mount Rushmore of female tennis players, McEnroe gave an honest view of the sport and shared his selections.
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Speaking to Rushmore, McEnroe said: "I would definitely put Serena [Williams] on there. I mean, in addition to the serve being the greatest serve in the history of women's tennis and one of the greatest servers period, she's one of the greatest competitors period.
"One of the all-time greatest athletes, male or female, of the last 100 years. And in addition to that, the heart, that will. Very intimidating in so many different ways. I could see how difficult it would be to have to play against her."
He continued: "The next person would be Steffi Graf, who I consider possibly as good as or better athletically as anyone I've ever seen in a man or woman in the sport of tennis. Unbelievable.
"We actually played mixed doubles once. That's a whole other story. But we did practice when we were both sort of at our best, and she was great in practice. The focus was there, the athleticism, intensity.
"She's got a lot of those attributes that Serena had, but you need in order to have the type of success they had. 24 majors, 22 majors, that's just singles."
The American continued: "My third is Billie Jean King. Because I think single-handedly out of the last 100 years she's done more for women's sports than any person on this planet.
"And also she's an incredible tennis player. And in addition to that also what went on with Riggs [Battle Of The Sexes]." Just her combination between her talent and also drive to make women treated equally.
The former world number one then completed his list by adding: "Martina Navratilova would be my fourth pick. Not only because she was a fellow lefty but because she was an incredible player.
"I believe the same amount of singles majors as Chrissie Evert. They played 80 times, which is unheard of. I believe that Martina had an edge, 43-37.
"I chose her because, even though I love Chrissie, Martina when she came into the sport, she had to defect and leave at like 16/18 years old, leave her family and suddenly she's on her own.
"In addition to that, which is tough enough and to try to be the best player in the world, to play the Chris Everts of the world, she lost all her sponsorships because she came out and said she was gay.
"So she lost all that, but she continued to forge ahead. Lost all her sponsorships and everything, and people looking at her, that to me is extremely difficult to do."
McEnroe was also asked about the current generation of WTA players, which includes Aryna Sabalenka, Elena Rybakina, Iga Swiatek, Coco Gauff and Jessica Pegula.
When asked if any of today's players could make his list a decade from now, McEnroe didn't hesitate: "Yeah. I would say that there's certainly an argument if Sabalenka keeps moving along at the pace she has the last couple years.
"And also Rybakina to me has got the best serve I've ever seen other than Serena."
It's a view that holds weight. Sabalenka currently sits atop the world rankings, while Rybakina has been widely recognised as one of the top servers in women's tennis.
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