France flyhalf Romain Ntamack will undergo a scan on his knee on Monday to see if there is any serious damage after limping off in their warm-up test against Scotland on Saturday, officials said.
The loss of the flamboyant pivot would be a major blow to the French ahead of their hosting of the World Cup, which kicks off in four weeks.
“Romain underwent a small hyper extension of the knee. We preferred to take him out of the game so there could be no further damage,” explained coach Fabien Galthie.
France also lost prop forward Cyril Baille to a calf injury as they scraped a 30-27 victory over the Scots at the Stade Geoffroy-Guichard.
France let slip a 27-10 lead after scoring two quick tries at the start of the second half, allowing Scotland to storm back and score three tries of their own in the last 20 minutes to level the score at 27-27.
A scrum infringement, however, handed France a penalty two minutes from the end which Thomas Ramos kicked over for victory.
“It remains a preparation match, with a different team from last weekend, who played together again for the first time since the end of March,” added Galthie.
“The Scots have a month and a half of preparation more than us because they finished their Championship in mid-May. Our goal is to continue preparing for a month and, even during the pool phase of the World Cup, there will be work to ramp up.”
It was the second successive Saturday that France played Scotland, and they had put out a second-string side at Murrayfield last weekend and lost 25-21.
But the team for the St Etienne clash was close to full strength.
“We have seen what we are capable of doing and had some highlights which allowed us to score to win the match,” the coach added.
Galthie said his side’s fatigue was to blame for the Scots storming back and almost snatching victory near the end.
“We were also taken aback at the start of the match but the second half gave us a glimpse how we can be successful.”
France play another warm-up test against Fiji in Nantes on Saturday and then meet Australia in Paris on Aug. 27.
Their first game at the World Cup is the opening match at the Stade de France against New Zealand on Sept. 8.