The province climbed to third in the RaboDirect PRO12 table with a convincing 37-7 win over Italian outfit Zebre at the weekend.
That made it four wins from their last five in the RaboDirect PRO12 for the defending European champions ahead of their two crunch clashes with Clermont at the Stade Marcel Michelin on Sunday and the Aviva Stadium the following weekend.
The French side have ten points from their two Heineken Cup outings while Leinster are lagging behind on eight.
However Clermont tasted defeat at the hands of Toulouse in the Top 14 on Saturday, and Sexton insists Leinster must keep their momentum going.
"Our whole season depends on these two games," said Sexton. "This is probably our biggest challenge, I'd say ever.
"It is always this important when it comes to the Heineken Cup.
"In different circumstances we'd probably be happy to come away from France with one point (losing bonus) and take four from our home game, but we probably need to win in France too.
"Clermont are on ten points so the losing bonus point might not do us.
"We're going to need the younger guys to step up to the plate and for everyone to play to their potential and have one of their best games in a Leinster jersey.
"And even then it might not be good enough.
"We won't get too many chances in Clermont's 22 so when we do we need to take them.
"We played there a couple of years ago and we were in their 22 and didn't take that chance. They immediately went up the other end and got a try."
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