Biarritz and France fly-half Julien Peyrelongue will be out of action for at least three months due to knee ligament damage.
The 23-year-old, who has been capped six times for Les Bleus, initially thought that the injury would sideline him for just two months.
Although Peyrelongue is now out of the entire RBS 6 Nations campaign, he is relieved that he will not need an operation to correct the problem which he sustained up during Biarritz's 48-17 European Cup win at Calvisano on Saturday.
"If the cruciate ligament had been affected I would have had to be operated on and my season would have been over," said Peyrelongue.
"But at least I am avoiding the operation. The doctors will put a splint on which I will have to keep for a month and then I will spend three weeks in a physiotherapy centre in Brittany."
Peyrelongue is targeting a return to action at the end of March.
"I will hopefully play with Biarritz in the European quarter-finals at the start of April, if we qualify of course," he added.
"I'll also play the last Top 16 matches. As for the Six Nations however I guess this is over."
France coach Bernard Laporte is already sweating on the fitness of Les Bleus' other fly-half Frederic Michalak, who faces at least a month out after injuring his right ankle against Stade Toulousain at the weekend.
France will kick off their defence of their RBS 6 Nations crown against Scotland on February 5.
England flanker James Haskell insists he will be pushing as hard as possible to be back from a toe injury in time to make his case for a spot in Eddie Jones' side looking to defend their RBS 6 Nations title next year.