Phelps, the most decorated Olympian of all time, compared the controversy surrounding Thomas to doping, saying he doesn’t believe he’s competed in a clean field in his entire career.
“I think this leads back to the organizing committees again,” Phelps told CNN’s Christiane Amanpour on Thursday. “Because it has to be a level playing field. I think that’s something that we all need. Because that’s what sports are and for me, I don’t know where this is going to go. I don’t know what’s going to happen.”
Thomas has been dominating the pool in swimming competitions this season. She previously competed for three years on the school’s men’s team, though her success this year ignited criticism over allowing transgender women to compete against biological females.
Women’s sports advocates and parents at Penn have recently spoken out against the NCAA and its rules on transgender student-athlete participation, which require trans women athletes to undergo at least a year of testosterone suppression treatment before competing on a women’s team.
Thomas switched to the women’s team in 2020 and has been receiving the treatment for nearly three years.
On Thursday, Phelps said that athletes should be able to feel comfortable in their own skin, but that sports should be played on an “even playing field.”
“I don’t know what it looks like in the future. But it’s hard. It’s very complicated and this is my sport, this has been my sport my whole entire career, and honestly, the one thing I would love is everybody being able to compete on an even playing field,” Phelps said.
Thomas will compete at next month’s Ivy League championships. She has already qualified for the NCAA championships in March.
Fox News’ Jessica Chasmar contributed to this report