Serena Williams and Roger Federer
Serena Williams and Roger Federer have won a combined 43 Grand Slams with four of them coming since the start of 2017. Pictured: Wimbledon Singles Champions Serena Williams and Roger Federer attend the Wimbledon Championships 2012 Winners Ball at the InterContinental Park Lane Hotel on July 8, 2012 in London, England. Clive Brunskill/Getty Images

Serena Williams might well be the greatest tennis player of all time regardless of gender according to Roger Federer.

Williams is arguably the most popular women's player in the last two decades as she has dominated her respective circuit for the majority of her career. Her last big triumph was at the Australian Open last year where she defeated her sister Venus to win a 23rd Grand Slam — just one away from equaling Margaret Court's record.

Following maternity leave that followed soon after, Williams returned to action in March where she recorded two wins and two losses before taking another break, but, will compete at the French Open which begins Sunday.

As she looks to reclaim her throne as the best women's player in the world at the age of 36, Federer could only show his admiration for the American's career and how she went on to become one of the greatest, if not greatest player of all time.

"[Williams’ career] has been fascinating to watch," Federer said in an interview with the Wall Street Journal. "She had a totally different upbringing — I came up through Switzerland with the federation, she did it with her dad and her sister."

"It’s an amazing story unto itself — and then she became one of the greatest, if not the greatest tennis player of all time," Federer said, adding that he was talking about the overall best, regardless of gender.

Federer is no stranger to the conversation as he is arguably the greatest tennis player of all time himself with 20 Grand Slam titles, 97 career titles and a number of records to his name including the most consecutive weeks (237) as the No. 1 male player in the world.

"But we know [Williams] is all the way up there. I’m probably up there with somebody, somehow," he added. "Maybe there’s a group, a best of five — and if you’re in that group, you should be pleased and happy. Tennis is a funky sport when it comes to that stuff."

The Swiss legend notably went nearly five years without a Grand Slam before experiencing a career resurgence since the start of 2017 as he went on to win three Grand Slam crowns and an overall total of nine titles since, while becoming the oldest No. 1 in tennis history earlier this year.

Turning 37 in August, retirement has always been a big question for Federer but he reiterates that he's not thinking about it so as long as he still enjoys playing the sport, though he acknowledges his career likely won't have a fairytale ending.

"I’ve long given up that it needs to end in a fairy tale," he explained. "I don’t need to be ranked [No. 1] or need it to be after a big title. If it happens that way, that’s amazing. But you can’t control it all. You have to put yourself out there, be vulnerable. I play because I love tennis, not because it needs to end [perfectly]."