Mikaela Shiffrin, the two-time Olympic champion skier and a top U.S. medal contender at the Winter Olympics in Beijing, said Monday that she has tested positive for the coronavirus and will miss World Cup races Tuesday and Wednesday in Lienz, Austria.

The result complicated Shiffrin’s preparations for the Beijing Games and showed how a surge of cases among competitors could upset China’s and the International Olympic Committee’s efforts to run virus-free Games inside an Olympic bubble. The Olympics are the greatest stage for many athletes, and a positive test can mean the loss of a rare opportunity, just as an outbreak in China could affect the entire Games.

Shiffrin’s announcement came several days after she won a giant slalom race in Courchevel, France, her 72nd career World Cup victory. Shiffrin leads the overall women’s World Cup standings and is first in the giant slalom and second in the slalom.

“I wanted to let you all know that I’m doing well, but unfortunately I had a positive COVID test,” Shiffrin, 26, wrote on Instagram. “I am following protocol and isolating.”

After her win in Courchevel on Dec. 21, Shiffrin spoke of feeling tired.

“It was really quite difficult, to be honest — tiring today! Even after the first run, I wasn’t sure I could do the second run,” she said. “It’s a big push and for every athlete racing. We had to dig very deep and just fight and be aggressive.”

On Instagram on Monday, Shiffrin wished her teammates luck in the races in Austria. “I’ll be cheering for you from afar,” she said.