The sports broadcaster said Garcia tested positive for the banned performance-enhancing substance Ostarine on the day before the April 20th bout in New York as well as on the morning of the fight.

ESPN boxing reporter Mike Coppinger added that Garcia also screened positive for another banned substance, 19-norandrosterone, although that result was described as "unconfirmed".

The details of the test results were contained in a letter obtained by ESPN by the Voluntary Anti-Doping Association (VADA), which oversees drug testing in boxing and mixed martial arts.

Ostarine is a drug used to prevent muscle loss and improve lean body mass and is used in the treatment of women with breast cancer.

Garcia, 25, scored an upset win over Haney after knocking him down three times during the fight on his way to a majority decision win.

Haney's title was not at stake because Garcia was 3.2 pounds over the limit at the weigh-in.

Garcia meanwhile denied wrongdoing in a profanity-laced post late Wednesday on X, formerly Twitter, describing it as "fake news".

"Everybody knows that I don't cheat," Garcia said. "What can I say? Why didn't they come out with this before the fight if they found it before? Why would they let me step into the ring as a cheater and then come out with a victory and post this."

He added: "These are people that are trying to attack me for whatever reason... I've never taken a steroid in my life, I don't even know where to get steroids at the end of the day. I barely take supplements."

In a separate post, Garcia appeared to suggest a tainted herbal supplement was to blame for the test result.

"My bad I shouldn't have took this," Garcia wrote above a photo of a bottle marked "Ashwagandha Root."