Thomas, a transgender swimmer on the women’s team at the University of Pennsylvania, previously spent three years competing on the men’s team.

She has become the topic of debate among those questioning trans participation in sport, with Phelps now weighing in on the topic.

The 36-year-old, who is the most successful and most decorated Olympian of all time, compared the discussion surrounding Thomas to that of doping in sport and stated that he has never competed in a “clean field” in his “entire career”. “I think this leads back to the organising committees again,” he said in an appearance with CNN’s Christiane Amanpour last week. “Because it has to be a level playing field.