France scrum-half Antoine Dupont may have broken his jaw in a high tackle that forced him off the pitch in the 96-0 World Cup thrashing of Namibia on Thursday, coach Fabien Galthie said.
The influential Dupont, who had earlier scored a try, left the pitch in Marseille in the 46th minute nursing his right cheekbone after Johan Deysel made a badly-timed head-on-head tackle and was sent off.
"We have a suspected cracked or fractured jaw. We will wait for scans before moving forward," Galthie told France 2 television.
The loss of 26-year-old Dupont, widely regarded as one of the best players in the world, would be a severe blow to host nation France's chances of winning the Rugby World Cup for the first time.
Namibia coach Allister Coetzee called Deysel's tackle an "unfortunate accident".
"This is the way the game's going," said ex-Springbok coach Coetzee. "It's unintentional, it happened so quickly.
"Dupont is not the tallest guy. Johan is a clean player, he's got no record of cards in the past, and he's a great defender.
"It's not unfair, but it's a pity it happened to him. He's the captain, he's a brave player, he's the glue of the team and he feels it."
Coetzee added: "It was an accident, an unfortunate one and we had to take that on the chin. He's cut up right now."