He had hoped to return for the semi-final in Bordeaux against the defending champions but instead faces a race against time to fit by the end of the season.
Clermont and Leinster know each other well having faced off in each of the last two seasons while Joe Schmidt - head coach with the Irish province - was formerly an assistant to Clermont boss Vern Cotter.
And Aurélien Rougerie - who will lead Clermont in the semi-final admits it will be a huge test for his compatriots.
He said: "Even before last weekend's Top 14 game against Montpellier we had already had a quick look at Leinster's quarter-final against Cardiff Blues.
"We already knew a fair bit about this team because we played them last year during the pool stage.
"They have quality players everywhere but their biggest strengths are probably the back row and their backs who are very fast - it will be a huge challenge to face Rob Kearney, Brian O'Driscoll and Gordon D'Arcy.
"And one thing that is sure is that their experience could work against us and they are so used to these games and if we are leading the game they won't panic.
"They showed this ability in last year's final against Northampton. It is a huge strength when you know how vitally important the details are in a Heineken Cup semi-final."