Renato Sanches, Jonathan Ikone and Jonathan Bamba have contracted coronavirus, Lille coach Christophe Galtier has confirmed.
The trio tested positive for COVID-19 and were absent from Lille's 2-1 friendly victory over Mouscron on Saturday.
Galtier said the players were infected during a recent eight-day rest period.
"Renato is in Portugal. He must undergo two negative tests to be allowed to travel," said Galtier.
"As for the two Jonathans, they are in France and will soon be back with the team, probably this Monday.
"After the first phase of training there were eight days of rest, and during those eight days the players contracted the virus.
"The players are fine, but we are waiting to see the results of the next tests."