Swimming legend Michael Phelps has given his opinion on the participation of transgender athlete Lia Thomas in NCAA events.Thomas has been the subject of widespread controversy since setting a number of records for the University of Pennsylvania last year.The 22-year-old, who began to transition in May 2019, meets the eligibility standards set by the NCAA for women’s swimming events, but this has not stopped a deluge of criticism about her participation.Phelps, the most decorated Olympian of all time, was asked about the topic during an interview with CNN, giving a somewhat ambiguous answer."I can talk from the standpoint of doping," he said. "I don't think I've competed in a clean field in my entire career."So, I think this leads back to the Organising Committees again, because it has to be a level playing field. I think that's something that we all need."I don't know where this is going to go. I don't know what's going to happen. I believe that we all should feel comfortable with who we are in our own skin. But I think sports should all be played on an even playing field."

Phelps continued: "I don't know what that looks like in the future. But it’s hard. It's very complicated.

"This is my sport. This has been my sport my whole entire career. Honestly, the one thing I would love is everybody to be able to compete on an even playing field. That's all I can say."

During his successful career, the 36-year-old Phelps earned 23 Olympic gold medals in swimming, and 28 Olympic medals in total.

Since making headlines around the world, Thomas has been backed by equal rights activists, the Ivy League, and the University of Pennsylvania.

"The Ivy League reaffirms its unwavering commitment to providing an inclusive environment for all student-athletes while condemning transphobia and discrimination in any form," a statement from the group of colleges and universities in the northeastern United States said.

The topic of transgender athletes in sport is a much-discussed one in the United States, particularly after nine states, including Texas and Florida, recently decided to ban transgender athletes from competing in female sports at schools.

The legislation, which applies to public school teams through high school, is part of a national campaign introduced by Republicans in 32 states. They claim it is protecting fair competition.

But, equal rights activists have argued there is no evidence that trans women and girls are dominating sports.

Ricardo Martinez, chief executive of the LGBTQ rights group Equality Texas, called the bill a "hateful, targeted attack on transgender people."