Junior lightweight contender Mikaela Mayer has tested positive for COVID–19 and won’t fight in the co–main event of Las Vegas’ first major boxing card since the start of the coronavirus pandemic.

Mayer announced her positive test on social media Sunday, two days before her scheduled bout against Helen Joseph in the Top Rank show at the MGM Grand Garden Arena on Tuesday night.

Mayer (12–0, 5 KOs) is a former U.S. Olympian and a rising star in the 130–pound division. Mayer is asymptomatic, but she tested positive for the virus on Saturday, she says.

“The rest of my team tested negative and they are all in good health,” Mayer said. “I was really looking forward to bringing back boxing for all of you and I’m disappointed for myself, my team, my supporters and for my opponent.”

Mayer was scheduled to face Joseph in a 10–round bout as she angles for a world title shot later this year.

The bout cancellation is the second in three months for Mayer, who hasn’t fought since October through no fault of her own. She was scheduled to fight Melissa Hernandez in New York on the undercard of a show featuring Michael Conlan in March before the pandemic forced its cancellation.

“After two hard back–to–back camps, not being able to step in to the ring both times, you can imagine how disappointed I am,” Mayer said. “However, these protocols were put into place for a reason and it’s more important to care about the health and well being of my team and the people at this event.”

The Nevada Athletic Commission mandated strict health and safety protocols when it allowed the return of combat sports late last month. UFC has followed those testing procedures and safety measures during its two shows at the gym on its corporate campus, and Top Rank has done the same in its plan to hold two boxing shows in the upcoming week.

Tuesday’s show will be headlined by unbeaten WBO featherweight champion and U.S. Olympian Shakur Stevenson against Puerto Rico’s Felix Caraballo.