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.
Peter O'Mahony was named man of the match against England last month
21 April 2017, 7:22pm
Peter O'Mahony's performance in the RBS 6 Nations finale for Ireland against England was crucial to his selection for the British & Irish Lions on Wednesday, Ireland and Lions defence coach Andy Farrell has revealed.