Sources: France fear ACL tear for L. Hernandez
Do France rely too heavily on individuals? (1:26)
Lucas Hernandez's World Cup campaign appeared in doubt after the France defender sustained a knee injury in the defending champions' 4-1 win over Australia in Group D on Tuesday.
"He needs to do some tests but it seems pretty serious. That's the big black spot tonight," said coach Didier Deschamps.
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Sources told ESPN that there were fears Hernandez had suffered a rupture of his anterior cruciate ligament (ACL), however it was too early for a full diagnosis.
Hernandez limped off the pitch after staying on the grass for a couple of minutes holding his knee after being beaten to the ball by Mathew Leckie, who delivered the cross for Craig Goodwin's opening goal for Australia.
He was replaced by his brother Theo Hernandez.
France have already seen several key players be ruled out of the World Cup ahead of the defense of the title they won in Russia four years ago.
Ballon d'Or winner Karim Benzema is missing the tournament with a knee injury suffered in training on Saturday, following on from fellow striker Christopher Nkunku, defender Presnel Kimpembe.and long-term absentees Paul Pogba and N'Golo Kante.
France lead Group D with three points, two ahead of Tunisia and Denmark, who played out a goalless draw on Tuesday.
Information from Reuters was used in this report.