Vincent Zhou, an American figure skater and two-time Olympian who was expected to compete in the men’s short competition on Tuesday, tested positive for the coronavirus on Monday, putting his ability to compete in jeopardy.

Zhou is undergoing further tests to confirm the positive result. If he tests negative, he will be allowed to compete.

Athletes and other attendees inside Beijing’s “closed loop,” a set of designated venues and hotels that visitors cannot leave, are required to undergo a polymerase chain reaction, or P.C.R., test every day. Of the 74,603 tests taken in the closed loop on Sunday, 13 people tested positive, including five athletes and team officials.

Some athletes arriving in Beijing have initially tested positive, forcing them to isolate in hotel rooms, but later produced negative tests that allowed them to compete. That group includes Elana Meyers Taylor, an American bobsledder who had been picked as the flag bearer at the opening ceremony; and Tahli Gill, an Australian curler who rotated between negative and positive tests after contracting the virus in December.

Thus far, the Olympics have successfully avoided a nightmare-scenario outbreak. A consistent trend has developed in the run-up to the Games and the first week of competition: A relatively small number of people have tested positive and been forced to isolate after arriving at the Beijing airport, while a tiny fraction of the overall Olympic population have been positive.

All international arrivals are tested at the Beijing airport and then isolate in hotel rooms until the results come back a few hours later. On Sunday, 11 of 142 people arriving in Beijing tested positive, including seven athletes and team officials, Olympic officials said.

Those who test negative are allowed to move freely throughout the Games’ closed loop. Those who test positive but do not require medical treatment must isolate in hotel rooms. They are allowed to return to action only after registering two negative tests.