Ukrainian tennis player Marta Kostyuk has made eye-popping accusations against the world’s top-ranked female tennis players, suggesting “some have a higher level of testosterone.”

When asked by Tennis 365 at the Wuhan Open if she feels “intimidated by players” such as Aryna Sabalenka and Iga Swiatek, the world Nos. 1 and 2, respectively, Kostyuk looked to “biological structure” as she expanded on the disadvantages she encounters when competing against the best of the best.

“We all have our own biological structure. Some have a higher level of testosterone, some have lower. It’s just natural and that definitely helps. I feel smaller than them. I try to see how I can beat these players with the tennis skills I have, but I have to work harder to win the points. I have to run a lot more than them to win points,” the 23-year-old athlete said in an interview published Sunday.

Kostyuk, who is ranked No. 27, was also asked what separates her from Swiatek, 24, and Sabalenka, 27, and cited their size.

“Against Iga, when I have played her, I wasn’t ready to play her at all. I played her over a year ago and she was very strong. With Aryna, I know it is a tough battle. I have my own skills, but at the end of the day, they are all much bigger than me, much taller than me, much stronger than me,” she said.

Kostyuk stands at 5-foot-9, according to her WTA profile, while Swiatek, who hails from Poland, is listed as 5-foot-9 as well. The Belarusian Sabalenka stands two inches taller at 5-foot-11.

Sabalenka faced Kostyuk twice this year, defeating her in the Round of 16 at the Internazionali BNL d’Italia and in the quarterfinals at the Madrid Open.

Outside of the physical, Kostyuk also addressed the emotional element of the sport and how her competitors have navigated that.

“Their confidence is just different. I have played some close matches against Aryna and you see how she plays the break points. She just doesn’t care. She has no doubt that she will save them. She hits a big serve and hits the forehand. No doubt. She is No 1 in the world, she has played a lot of finals and she has that confidence. That helps her to have no doubts. For me, it is not so easy for me to play without doubt. It is an interesting sport and I’m enjoying the journey of trying to figure it out,” Kostyuk said.

Kostyuk’s comments unsurprisingly stirred buzz after the interview’s release, with some online speculating if Sabalenka clapped back via a series of bikini snaps.

The four-time Grand Slam champion, who is less than two months removed from her U.S. Open triumph, shared a collection of Instagram snaps Monday that featured her modeling a two-piece at the luxurious Atlantis The Royal Dubai resort.

“Much needed girl’s day with my bestie,” Sabalenka captioned the post that featured fellow tennis star Paula Badosa.