Lionel Messi is among four Paris St Germain players who have tested positive for COVID-19.
Juan Bernat, Sergio Rico and Nathan Bitumazala, as well as one PSG member of staff, are also isolating after contracting the virus.
The 34-year-old Messi, who was recently crowned as the world’s best player for the seventh time with another Ballon d’Or award, used the winter break to return to his native Argentina.
Video has since emerged online of him attending a concert with his wife.
Head coach Mauricio Pochettino said on Sunday: “Leo Messi has been in regular contact with our medical team and when he has a negative test he will travel to France, and we do not know any more than that.”
PSG said in a statement that the players were subject to the appropriate health protocols ahead of the team’s French Cup tie at third-tier Vannes on Monday.
PSG will play their first Ligue 1 game of 2022 against Lyon next Sunday, but with former Barcelona captain Messi still in Argentina, he must be a significant doubt for that fixture.
“I do not know if he will be involved against Lyon,” Pochettino said. “Until Leo Messi gets a negative test in Argentina, he will not be able to travel to France.
“It is all down to the test in terms of when he can travel. When he does, we will assess when he is ready to play.”
Pochettino is expected to field a young side in tie at Vannes with Neymar also unavailable as he continues to recover from an ankle injury.
Pochettino said in a news conference: “We have been living with the virus for two years now, and I think we all know we need to avoid it.
“But it is a virus we have been living with for a long time and there is still a lot that we do not know about how it works.”