Warriors sit bottom of Pool Four with nothing to show for their first two encounters against Northampton and Ulster.
But should Gregor Townsend's men triumph over the French cracks, and back that up by completing a quick fire double over Castres in the return on Sunday week, they would be back in the hunt for a quarter-final place.
Cusack admits Glasgow's pride has been stung by their 31-3 hammering at the hands of Munster last Saturday in PRO12 action, but the powerhouse prop's is keen to quickly erase the pain of that defeat.
He said: "I am absolutely delighted to have signed the three- year deal and for me the best way to celebrate that would be to do everything I can to help Glasgow to a win on Friday night.
"Our pride has been hurt by what happened against Munster and we know we have a lot to make up for.
"We have to prove that last Saturday was a bad day at the office and this Heineken Cup tie with Castres is the perfect opportunity to prove that. Really, it is an all or nothing situation. If we get the win then we would be going to Castres having badly damaged them but also handed ourselves a life line.
"It would be a massive stepping stone and we know that we will have a big crowd out at Scotstoun on Friday night and that we owe them a win on home soil. We'll do everything to make sure we leave nothing in the locker."
When Cusack arrived at Glasgow two years back from Doncaster Knights, he came with a reputation as the best scrummaging tight-head in the English Championship and his form ever since has more than lived up to that accolade.
His demolition job on the Cardiff front row earlier this season was immense.
But now the Warriors pack will face the best scrum in French Rugby and if ever they needed a big performance from the Yorkshireman, Friday night is the time.
Cusack declared: "We know all about the reputation of the Castres pack, but we have held our own against Ulster and Northampton up front and we are determined to more than match Castres.
"For me this is exactly the type of game I came to Glasgow to play in and Friday night can't come quickly enough.
"Defeat is just not an option for us and this is a great chance to deliver the type of performance that will make the support proud to be Warriors fans."