Martina Navratilova does not believe transgender athletes should be able to compete against non-transgender women.
The former tennis star wrote an op-ed in the Sunday Times detailing why she feels the practice is unfair.
"It's insane and it's cheating. I am happy to address a transgender woman in whatever form she prefers, but I would not be happy to compete against her. It would not be fair," Navratilova wrote (h/t Frances Perraudin of the Guardian).
The 62-year-old came out in 1981 and has been a gay rights activist after her playing career, but she thinks men would force their way into women's competitions if transgender women are allowed to compete.
"To put the argument at its most basic: a man can decide to be female, take hormones if required by whatever sporting organization is concerned, win everything in sight and perhaps earn a small fortune, and then reverse his decision and go back to making babies if he so desires," she wrote.
Different organizations have different rules for eligibility, but the International Olympic Committee does require testosterone to be below a certain level in order for transgender women to compete.
This essay comes a few months after Navratilova first created controversy with a tweet in December.
"You can't just proclaim yourself a female and be able to compete against women," the 18-time Grand Slam champion wrote. "There must be some standards, and having a penis and competing as a woman would not fit that standard."
Her comment received backlash at the time and her latest article has brought on further criticism from the LGBT community.
"It's a wild fantasy worry that is an irrational fear of something that doesn't happen," world track cycling champion and transgender athlete Rachel McKinnon tweeted Monday. "An irrational fear of trans people? Transphobia."