Martina Hingis and Kim Clijsters are members of an exclusive club.
The Hall of Famers are among a handful of players to hold the world No. 1 ranking in both singles and doubles.
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The 39-year-old Hingis is rooting for the 36-year-old Clijsters in her planned 2020 return to the WTA Tour, but questions if the mother of three can make a successful comeback amid the physicality of today's tennis.
"To me, I think the game has evolved," Hingis told the media at the WTA Finals Shenzhen. "The last time she won was 2011 or 2013. It wasn't yesterday. After all of this, I mean, I played some exhibitions with her or against her, we also played in doubles, I think it's quite different.
"I mean, she was a much more physical player than I was. For me, the doubles was good enough. I felt like, This is what I can do, still participate. I finished at No. 1, so it was nice to come back and play. I felt like I would not be probably good enough for singles. Also I didn't want to put myself out there. That's why I said that it's quite ambitious to want to make that move."
Five-time Grand Slam singles champion Hingis mastered the art of the comeback. Hingis initially stepped away from the sport at age 22 before mounting a successful comeback in 2006.
The former No. 1 eventually worked her way back to No. 6 before retiring again on November 1st, 2007 following a hip injury and positive test for cocaine. Hingis launched another comeback in 2013. Playing exclusively doubles in her second comeback, Hingis won multiple Grand Slam doubles title and regained the world No. 1 doubles ranking.
The new mother suggests Clijsters will face a major challenge against younger players, including US Open champion Bianca Andreescu.
"Even for me it's going to be, like, interesting to watch," Hingis told the media at the WTA Finals Shenzhen. "If she can come back to the game she finished off with, then I'm sure she can have some good matches. Will that be enough to play in today's game? I don't know that.
"I mean, personally I can't see that she's going to go out there and beat Andreescu, Sabalenka, the people who qualified here. If she gets a chance, a good draw, she can get into it. Depends maybe on the first matches who she is going to face. As a wild card, if she's going to face Andreescu first round, you don't really know."
Though she suggests her fellow former No. 1 may struggle, Hingis said she's excited to watch Clijsters compete again.
"I think everybody was surprised to hear about that. She's 36 years old, three-time mother," Hingis said of Clijsters. "I think that's a very ambitious challenge to come back. But I'm sure she won't come back until she's ready. When she feels she's ready, she'll play some good tennis.
"I'm actually excited to see how she's going to do. I mean, speaking as a mother, it's not that easy after having a child and everything. Like I said, it's a very ambitious project. But I wish her all the best."
Photo credit: Christopher Levy