World number one Aryna Sabalenka weighed into the participation of transgender athletes in women's sport, saying it would be unfair for women to face "biological men" in professional tennis.

The WTA Tour Gender Participation Policy currently permits transgender women to participate if they have declared their gender as female for a minimum of four years, have lowered testosterone levels and agree to testing procedures.

These conditions may be further varied by the WTA Medical Manager on a case-by-case basis.

Asked about transgender athletes in an interview with Piers Morgan released on Tuesday, four-times Grand Slam champion Sabalenka said: "That's a tricky question. I have nothing to do against them.

"But I feel like they still got a huge advantage over the women and I think it's not fair on women to face basically biological men," added the Belarusian, who was on the show to promote her "battle of the sexes" clash with Nick Kyrgios on December 28.

"It's not fair. The woman has been working her whole life to reach her limit and then she has to face a man, who is biologically much stronger, so for me I don't agree with this kind of stuff in sport."

The WTA did not immediately respond to an emailed request for comment.

Former Wimbledon finalist Kyrgios said he agreed with Sabalenka, adding: "I think she hit the nail on the head."

There have been no examples of transgender players competing in professional tennis in recent years.

Transgender tennis player Renee Richards competed on the women's professional tour from 1977 to 1981, before coaching tennis great and gay rights trailblazer Martina Navratilova.

Navratilova, an 18-times Grand Slam singles champion, has been an outspoken critic of the inclusion of transgender athletes in women's sport.

Others, like Billie Jean King -- the 12 times Grand Slam singles champion who won the original "battle of the sexes" in 1973 -- see transgender exclusion as discrimination.

In 2024, Britain's Lawn Tennis Association updated its rules to bar transgender women from competing in national and inter-club female competitions.

In the past two years, several sports federations have launched their own studies or changed rules to ban anyone who has gone through male puberty from competing in the female category at an elite level.

Transgender advocacy groups say excluding trans athletes amounts to discrimination.

Critics of transgender inclusion in women's sport say going through male puberty imbues athletes with a huge musculo-skeletal advantage that transition does not mitigate.