Cotter's men scored two tries at Parc des Sports Aguilera, but found themselves outdone by the deadly accurate boot of Parra's opposite number Dimitri Yachvili, who kicked five penalties. And with Toulouse winning at Stade de France against Stade Francais Paris, the gap at the top of the Top 14 opened up to four points.
Clermont will be travelling for the fourth time in the Heineken Cup knock-out stages and will be seeking their first win on Sunday. It is a game that will feature some fascinating match-ups as both teams chase a possible home country semi-final against the winners of the game in Dublin between reigning champions Leinster Rugby and Cardiff Blues.
England duo Brad Barritt and Owen Farrell will face their French RBS 6 Nations foes Aurelien Rougerie and Wesley Fofana once again, Dave Strettle takes on All Black try machine Sitiveni Sivivatu on the wing and last season's Heineken Cup winner with Leinster, Nathan Hines, battles with new England lock Mouritz Botha up front.
"I'm anticipating Owen Farrell playing at No 10 against us after his great 6 Nations. Brad Barritt is another very good player and it should be a fascinating battle against Rougerie and Fofana," said Cotter.