"We cannot let Clermont take four more points. If we end up six points behind before the return at the Aviva, they will be too far ahead," he said.
The French club devoured The Scarlets at home and Exeter Chiefs away to amass a perfect 10 points from two games, while Leinster stumbled past Exeter at home and The Scarlets away.
"They accrued 12 tries in two days, while we have registered one. We have reason to be worried. But we must still have the ambition to win both games," said Schmidt.
The people of Clermont feel their team owe them the prestige of taking down the reigning European champions, having exited the Heineken to Leinster in two of the last three seasons.
"It will be very difficult to shake the (Stade) Michelin," added Schmidt. "But we must absolutely get back on equal points or surpass Clermont after this back-to-back confrontation."
At the minimum, Leinster must secure a losing bonus-point in restricting Clermont to less than four tries and then hit them for five without reply back in Dublin. This is the tallest of orders.
"If we lose to Clermont, we can still stay alive and hope to take one of the best runners-up places. But we lose control of our destiny. To avoid this, the simplest calculation is to win. But it is easier said than done," he added, in what can only be described as an understatement.
"Clermont have not lost at Michelin for three years now. If we do not play at our best, we will not win. We know that these next two matches will determine our future in Europe this season."
It is no secret that Leinster have struggled for consistency this season and will travel to the Massif Central without the moved-on Brad Thorn and three top-class international backs.
"This week promises to be quite intense and high in emotion. I expect my team to produce its best game of the year on Sunday at Michelin," he said.
"We know it will be very difficult and we won't have all our weapons since neither (Brian) O'Driscoll (ankle) nor (Rob) Kearney (back), or (Luke) Fitzgerald (knee) will be present at Clermont.
"Our team will, by this fact, not be as strong as that of last April. These three players bring such experience and talent. They may be sorely missed. We have to find solutions to compensate for their absence."
The solution could come in the front row, where Leinster have registered Ireland international tight-head Michael Bent as one of two Additional Players allowed for the Heineken Cup.
It means Leinster will bring two complete international quality front rows to Stade Michelin.
The other Additional Player, Andrew Goodman, was paired with Gordon D'Arcy in a new centre partnership against Zebre last Saturday.
The 6'2," 16-stone-10 New Zealander would give Leinster the option to take the ball up closer to the action and provide a second kicking option to Jonathan Sexton.
The solution could be to surprise the French by keeping it tight.