Former Wimbledon champion Martina Navratilova has sparked a row among the transgender community after she posted a tweet claiming that “having a penis and competing as a woman” is not acceptable in sports, as she felt that men who challenge women in games have an unfair physical advantage.

Responding to a question from one of her followers about transgender women in sport, Navratilova said, “Clearly that can’t be right. You can’t just proclaim yourself a female and be able to compete against women. There must be some standards, and having a penis and competing as a woman would not fit that standard.” As a result of the tweet, she has been accused of being ‘transphobic’ by Dr. Rachel McKinnon, a Canadian transgender activist and cyclist. “Genitals do not play sports. What part of a penis is related to tennis? How does that ‘level’ any playing field,?” she responded to Navratilova’s tweet.

The legendary tennis player, who has won a total of 18 Grand Slam singles titles including the Wimbledon women’s singles title nine times, has always been a supporter for a wide spectrum of LGBT causes, having declared herself a lesbian a few years ago.

Navratilova later responded to the criticism saying, “I am sorry if I said anything anywhere near transphobic – I meant no harm. I will educate myself better on this issue but meantime I will be quiet about it.” However, after a stream of critical tweets from McKinnon that almost bullied her into silence, the tennis champ added, “Rachel, you might be an expert on all things trans but you are one nasty human being.”

In the last few years, men who identify as females have won competitions against women in track and field, cycling, rugby, boxing, and MMA.