Halfback and star player Antoine Dupont looks set to miss France's Six Nations game against Scotland after testing positive for COVID-19.
All the players in France's 31-man squad have been tested and so far 11 have been negative, with Dupont the only one to return a positive test, the French federation (FFR) said in a statement on Friday.
France play Scotland at the Stade de France on February 28.
The FFR said that Dupont, the outstanding performer in European rugby over the past year, did not show any symptoms but he would be "isolated, in accordance with the sanitary protocol".
Health minister Olivier Veran announced on Thursday that anyone testing positive for COVID-19 would need to isolate for 10 days, instead of seven previously, as France looks to contain the emergence of a variant that first appeared in Britain.
The FFR had ordered further tests on the squad after saying on Tuesday that head coach Fabien Galthie, forwards coach William Servat and another staff members had also tested positive for the coronavirus.
All the players were negative on Tuesday but there were concerns about Dupont, who spent time in close contact with Galthie at an awards ceremony broadcast online on Monday, with neither of them wearing a mask.
Dupont, 24, was named player of the championship after last year's Six Nations, when France finished in second place.
Les Bleus lead the standings after two wins from two games, with Dupont setting up four tries in the opening match against Italy.