Gloucester and England No.8 Luke Narraway believes a loss against Cardiff will end their hopes of a place in the Heineken Cup quarter-finals.
The Blues currently have a 100 per cent winning record in this season's competition and are sitting pretty at the top of Pool Six. A win against Gloucester at Kingsholm will guarantee them a spot in the last eight.
Gloucester face the prospect of having to win both of their remaining matches to qualify as group winners.
"If we lose that will be us very much out of the Heineken Cup but win on Sunday and we will still be right there in the mix with a tough game at Biarritz Olympique to come in round six," Narraway said.
"The big thing is that our fate is totally in our own hands."
Narraway also thinks that Gloucester's passionate home supporters can will them to victory in the crunch clash.
He added: "Having the match at Kingsholm is a huge thing for us.
"The best club crowd I have played in front of was the one at Kingsholm for the Munster quarter-final tie last season and I see Sunday as having much the same atmosphere with most of the 16,500 crowd roaring us on."