After their defeat to Scarlets, Exiles' hopes of qualifying for the semi-finals depend on them beating Gloucester at the Madejski Stadium this Saturday (3pm ko) and Leicester not winning their home clash with Newcastle Falcons.
But although the focus is on progressing to the last four, Casey believes a win at the weekend is vital for both the short-term and the long-term.
"It's a massive game for us that we have to win, not just for the LV= Cup but also for our Premiership ambitions," he told the News.
"We have to put in a good performance against Gloucester. They are a decent side and are in contention to qualify as well so both sides will be going for the win. It might be out of our hands but we believe that we can win on Saturday and then we will see what happens."
Exiles would be in a far stronger position in their group had they taken their chances and beaten Scarlets in Wales last weekend.
Casey admits the defeat was 'devastating' for the team considering how well they played but says there were plenty of positives.
"We played well against Scarlets but we just weren't clinical enough with our opportunities. It's something we can't afford to dwell on and we're not too beat up about it now because we played good rugby and created enough opportunities to be 14 points ahead early on," he commented.
Casey is in his testimonial year with Irish before retirement this summer and is determined to end his spell at the Madejski with silverware.
"It would be amazing for me to win something in my final season with the club, it would be the perfect way to bow out," he said.
"But at the moment we can't look past Saturday, it's a game that we have to win to stand any chance of progressing in the competition and getting into the semi-finals."
With Casey set to end his career this summer, he believes he will be leaving Irish in good hands - but says it will be tough for the club to replace Toulon-bound Nick Kennedy.
Kennedy and Casey have been an integral part of the Irish second row and lineout since joining in the early 2000s, making nearly 450 combined appearances for the club.
But with 33-year-old Casey in his testimonial year before retirement, and Kennedy seemingly set to join French Top 14 side Toulon, Irish are going to have two very big holes to fill this summer.
"Nick will be a massive loss for the club," Casey said. "He has been one of the standout performers in recent seasons and has done the club a great service.
"He will be missed and will be very tough to replace but that's just professional sport, players move on."
By way of replacements, Irish have already secured the services of 6ft 6in forward George Skivington from Leicester Tigers and will be looking towards Matt Garvey and Bryn Evans to step into the holes left by Casey and Kennedy.
Garvey, 24, enjoyed a breakthrough season in 2010/11 and was named Irish's best defender with a tackle completion rate of over 95 per cent.
Behind him are a number of other talented youngsters on the fringes of the first-team squad and Casey thinks that with this group, Irish have a bright future ahead.
"The future at the club is definitely positive," he said. "There are a lot of very exciting youngsters here who are just starting their careers but are already in the London Irish picture.
"The LV= Cup has been a great opportunity for some of the players to get match time and the performances have been very encouraging from some of the youngsters. The competition has given some of the young guys the chance to play and they have stepped up."