But Wales star Byrne, 28, is now ready to make a shock Ospreys comeback in their 'must-win' Heineken Cup tie with Leicester Tigers on Saturday.
Ospreys coach Sean Holley said: "He's fit and we're hopeful he can play. He was in pain in Perpignan but he has steadily improved."
Byrne was named in Wales' 28-man squad for their opener against Scotland at Murrayfield on February 8.
And the Lions hopeful last night admitted his relief on an unexpected return to action.
"The ankle has improved quite a lot from the weekend," said Byrne.
"I've still got time on my side and I don't want to miss this game and the chance to be part of making history with the Ospreys."
Wales back-rower Jonathan Thomas is rated doubtful for the Pool Three clash at the Liberty Stadium following a troublesome groin problem.