(CNN) Tennis great Martina Navratilova has been criticized after claiming it is a form of "cheating" for transgender women to be allowed to compete in women's sport.

The 18-time Grand Slam winner wrote in The Sunday Times that it was "insane" that "hundreds of athletes who have changed gender by declaration and limited hormone treatment have already achieved honors as women that were beyond their capabilities as men."

This is not the first time Navratilova, a gay rights campaigner who suffered homophobic abuse when she came out in 1981, has caused controversy with her remarks on transgender athletes.

In December she was criticized after tweeting: "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."

Martina Navratilova won 18 Grand Slams during her tennis career.

Her comments led to her becoming embroiled in an online argument with cyclist Rachel McKinnon, the first transgender woman to win a world track cycling title in October 2018.

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