Alexandre Lacazette will undergo tests to determine the severity of a hip injury suffered during Lyon's resounding loss to Paris Saint-Germain in the Trophee des Champions.
Linked with a move away from Ligue 1 for much of the off-season, namely to Premier League outfit Arsenal, Lacazette was substituted at half-time of Lyon's 4-1 defeat to PSG on Saturday.
Lacazette refused to talk about the injury post-match but coach Bruno Genesio provided an update on the 25-year-old striker, with Lyon sweating on his fitness.
"It's worrying," said Genesio. "It's a big downside of the evening in addition to the defeat.
"This is our attack leader, he is needed.
"It's too early to tell about the injury. There will be examinations early this week."
Lyon president Jean-Michel Aulas added: "Lacazette has a hip pain. He must pass exams.
"Hopefully this is not very serious."
Lyon kick-off their Ligue 1 campaign away to Nancy on August 14.