Three members of Team GB in Rio have missed two whereabouts doping tests within the last 12 months, ITV News has learned.
The UK Anti-Doping agency (UKAD) has confirmed the details to ITV News.
One of them is cyclist Lizzie Armitstead - who won a court battle to compete in the Rio Games after being issued with three strikes for missed tests. The first incident was ultimately considered void.
The identities of the other athletes are not yet known. The athletes will remain anonymous unless a third whereabouts test is missed.
It means that all three are on their last chance under strict anti-doping rules to ensure sport remains clean.
Athletes can fail whereabouts tests if they are not available for tests or do not provide full details of their location at all times.
A missed test is recorded if they are unavailable for testing during a specific 60-minute slot.
Athletes may also be found in breach through a filing failure if they do not provide up-to-date details of their location.
Any combination of three missed test(s) and / or filing failure(s) within a 12-month period will constitute an anti-doping rule violation, the UKAD said.