The 32-year-old Wales suffered the injury in Clermont Auvergne’s 28-21 victory over Leinster in the Heineken Cup.
It is not yet known how long Byrne will be sidelined but he is likely to miss the Six Nations.
“He [Byrne] suffered a broken bone in his fifth vertebra,” read a Clermont Auvergne statement.
Byrne has not played for Wales since winning his 46th cap during last year’s World Cup.
He has since fallen behind Leigh Halfpenny and Liam Williams in the Welsh full-back pecking order.
But he has been in fine form for the French club and was eyeing a return to the international stage.
“I hoped I was playing well enough to push for a place in the autumn Tests but it wasn’t so,” said Byrne prior to the injury.
“All I can do is keep on putting in performances in the Heineken Cup and in the Top 14 and hope that someone is watching.
“You always want to play international rugby but at the moment I am loving my time at Clermont and if Wales doesn’t happen then there’s not much I can do about it.”
