Midfielder Houssem Aouar was ruled out of Lyon's first match of the Ligue 1 season against Dijon on Friday after testing positive for Covid-19, his club announced shortly before kick-off.
Aouar, 22, returned a positive result following a round of testing carried out on members of the Lyon squad and coaching staff on Thursday.
"The results received this morning by the medical management of the club revealed that Houssem Aouar is the only player in the squad to have tested positive for Covid-19," the club said in a statement.
"As soon as the results were made known, Houssem was put into isolation for a fortnight while still being completely asymptomatic."
Lyon added that Aouar would "return to training with the first-team squad in 10 to 15 days, depending on his next follow-up tests."
He has been withdrawn from the France squad he was named in Thursday by coach Didier Deschamps for next month's Nations League matches against Sweden and Croatia.
The uncapped Aouar will be replaced by former Lyon star Nabil Fekir, currently at Real Betis.
Manchester United midfielder Paul Pogba was omitted from the initial squad after he also tested positive for Covid-19.