The Irish province, who are now trailing by five points in the Pool, surrendered their 17-match unbeaten tournament run and know they need a victory in the home leg at the Aviva Stadium in Dublin.
The Dubliners know defeat would probably end their defence of the title which they have lifted in three of the last four years and seen them dubbed the best side the tournament has ever seen.
Clermont, who have never reached the final of this tournament, are most people's favourites to finally lift the Heineken Cup this season and they proved themselves worthy of the backing in their victory over Leinster.
A win for the French Top 14 side would put them in the driving seat of the Pool and would almost certainly see them get the added advantage of a home quarter-final place.
Clermont are on the verge of their fifth quarter-final place but have never reached the final of the Heineken Cup. Leinster have won three of the last four Heineken Cup finals.
• Nobody has made more offloads than Clermont's Aurelien Rougerie this season, the centre has made nine to date.
• Jamie Heaslip has made 40 tackles (0 missed) so far this season, more than anybody else.
• Clermont have averaged a team gain of 565 metres per match so far, the most in the tournament.
• This weekend sees the sixth meeting between these teams since 2010. The Irish outfit have won three of those and lost the other two.