Schmidt (above) returns to his former club knowing that his depleted squad cannot afford defeat against the formidable, full-strength Pool 5 leaders. "We know that we will be playing for our future in European competition over the next two matches," cautioned the Kiwi coach, whose side trail the French by two points.
"They have scored 12 tries in two games while we have registered one. We have reason to be worried! Apart from the win against Munster, we haven't been able to play for 80 minutes and produce a performance of the highest level."
Leinster beat Clermont in a classic semi-final last season on neutral French soil but the hosts will protect a remarkable 50-game unbeaten streak at their home ground on Sunday.
"If we do not play at our best, we will not win. I expect that my team will produce its best game of the year," added Schmidt, who is likely to spring the untested Andrew Goodman into midfield alongside Gordon D'Arcy.
"We are missing three top players. We need to find solutions to compensate for these absences.
"We cannot leave Clermont without the four points. If we end up six points behind heading into the following week, they will be too far ahead. We must have the ambition to win both games.
"If we lose to Clermont, we can still be alive and hope to take a second-place berth but we will lose control. To avoid this, the simplest calculation is to win."
Meanwhile, Clermont have revealed that prop Thomas Domingo is a major doubt for Sunday's showdown after damaging his knee in training.