London - British women's marathon world record holder Paula Radcliffe has warned of potential "manipulation" in top-level sport unless tighter rules are applied to transgender women.
International Olympic Committee guidelines state that athletes who transition from male to female should be allowed to compete without undergoing sex reassignment surgery but need to demonstrate their testosterone level has been below a certain level for at least a year.
The debate about whether it is fair for transgender women to compete in women's sport has come into sharp focus since a row developed between transgender cyclist Rachel McKinnon and former tennis player Martina Navratilova.
"Right now, transgender women are not a threat to female sport," Radcliffe told BBC Sport.
"But you would be naive if you thought that, by not putting in any rules, it couldn't come to that at some point in the future.
"People will manipulate this if there is an opening there to make money and win medals and we've seen the lengths people go to, the lengths Russia went to cheat in sport. "
Radcliffe said it was important to protect female sport but also transgender women and their rights.
"You don't have to talk about excluding transgender women from sport, but I don't know if the current levels go far enough. I'm not an expert, but I'm trying to safeguard the future of female sport," she added.
"I think 10 (nanomoles of testosterone per litre, the current IOC requirement) is too high given I've read that the normal female range is up to two. So five might be about right.
"Both sides need to be protected, and calm, scientific research needs to be done. You can't have the two sides doing the research. It has to be neutral."
Radcliffe also called for a halt to the "attacking and bullying" that she believes has existed between groups and individuals with contrasting views.
Navratilova, an 18-time Grand Slam title winner, was branded "transphobic" after writing in a newspaper column that allowing trans athletes to compete with women who were assigned female at birth is "cheating" and "unfair".
She apologised for describing transgender athletes wishing to compete in women's sport as cheats but said the issue of transgender athletes was guaranteed to keep raising competitive as well as ethical questions.