Team Ireland athletes have been told that a positive Covid-19 test at this stage would signal the end of their Olympics hopes.
The Games are under way in Tokyo and scheduled to be complete on 8 August.
The first Irish in action, the rowers, start their campaigns on Friday morning with gymnastics, cycling, boxing, taekwondo, dressage, swimming events also taking place tomorrow.
The hockey team play their first pool game against South Africa on Saturday.
Tokyo 2020 Olympic organisers said on Thursday morning that two athletes residing in the Olympic Village tested positive for Covid-19.
They announced 12 new positive cases overall, including the two athletes, bringing the total to 87.
Olympic Federation of Ireland chief executive Peter Sherrard told RTÉ's Morning Ireland that the athletes have been informed what is likely to happen.
"A positive test would probably be their Games over," he said.
"It depends on the number of days they have until competition.
"So, if they were able to test negative, generally after 14 days, they could potentially compete but in reality it would have a very serious detrimental effect on performance.
"In reality, we’ve also explained to the athletes that it’s more likely than not to lead to their Games being over if that was the case.
"In the case of a close contact, it’s not quite the same.
"It’s daily PCR testing and the Games’ organisers have indicated quite strongly that they feel that if daily PCR tests are being passed and there is an ability on their part to allow that athlete to compete, they’ll try to do so but there’s no guarantees with that either."
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