Wasps, the 2004 Heineken Cup winners, could secure quarter-final status by defeating their French opponents and Pool One rivals Castres suffering a shock defeat against already-eliminated Treviso in Italy.
Reality though, suggests Wasps will need victory on Saturday - and possibly in Castres on Saturday week - to reach the knock-out phase following two seasons of pool stage failure.
McGeechan's team selection reflects his determination to get part one of the job done, rolling out a pack containing eight internationals - Tim Payne, Raphael Ibanez, Phil Vickery, Simon Shaw, Tom Palmer, Joe Worsley, Jonny O'Connor and skipper Lawrence Dallaglio - for the visit of Perpignan.
Wasps were beaten 19-12 by Perpignan in a dire game almost three months ago, yet they have not lost a Heineken Cup home tie since late 2004.
Rugby director McGeechan said: "This is obviously a massive game for the players and the club.
"We are going head to head with Perpignan for a chance to progress to the knock-out stages of the tournament, and so we have to adopt a cup final-type mentality for the game.
"We are lucky that the squad is in good health and ready to play, but we have worked carefully to manage the players though the heavy Christmas programme to get to this position.
"Therefore, we have been able to select from an almost full-strength squad, and in particular, we have a very experienced pack to face Perpignan."
Leicester are hurtling towards a Pool Four decider against reigning European champions Munster in Limerick on Saturday week, but they cannot allow such an enticing prospect to overshadow their Welford Road appointment with Cardiff Blues.
Home defeats at the hands of Leicester and Munster effectively destroyed Cardiff's quarter-final ambitions, and Blues lock Scott Morgan admits "payback" is a motivating factor for the Welsh region on Saturday.
Morgan said: "We were bitterly disappointed after Leicester won such a tight game against us at the Millennium Stadium in October.
"It has made the season a lot harder for us, and we definitely want a bit of payback for what they did to us in Cardiff.
"I was a Bristol player when we beat Leicester (at Welford Road) in 2002, and there is nothing better in a rugby player's career than winning up there in front of 16,000 fans.
"But there are few tougher places to win. You know what to expect, you just have to work really, really hard for everything you get."
Cardiff are without suspended Wales flanker Martyn Williams, but Tigers have lost fly-halves Andy Goode (hamstring) and Paul Burke (knee) to injuries, so Ian Humphreys wears the number 10 shirt in a team of 12 internationals captained by Martin Corry.
English champions Sale Sharks must secure a bonus point triumph against hapless Italian outfit Calvisano on Saturday to keep alive any hope of progressing from Pool Three.
Richard Wigglesworth is pressed into emergency fly-half duty at Centro Sportivo San Michele with Charlie Hodgson, Lee Thomas and David Blair all out injured, while Ben Foden partners him at half-back, but a handful of rested players include Sebastien Chabal, Sililo Martens and Juan Martin Fernandez Lobbe.
Sharks coach Kingsley Jones said: "It was important that we rest some players this week following the Christmas and new year schedule, but it was important to name a team that could attack and score tries."
London Irish welcome back fit-again Argentinian recruits Juan Leguizamon and Gonzalo Tiesi against Madejski Stadium visitors Toulouse on Saturday, but Pool Five is totally in the hands of Llanelli Scarlets.
Llanelli, who took charge of the group by inflicting back-to-back defeats on Toulouse before Christmas, need victory against Ulster in Belfast on Saturday or Irish at Stradey Park on Sunday week for guaranteed top spot.
The Scarlets though, will need to recover quickly from a miserable run of three Magners League defeats during the holiday period when they came unstuck against Ospreys, Cardiff and Edinburgh.
Scarlets centre Regan King said: "With all the hard work we have done, failure now would be unthinkable.
"Results have not gone our way in the Magners League, but we have to forget that and get our show back on the road quickly. We must win in Belfast.
"It is an exciting time to be on the verge of our first quarter-final for three years. It is at the back of our minds all the time but first and foremost we have to get there."
Elsewhere on Saturday, Pool Two leaders Leinster host Edinburgh, while Sunday's action sees a pivotal Pool Three contest between the Ospreys and French Championship leaders Stade Francais at Liberty Stadium.
Ospreys wings Shane Williams (ankle) and Nikki Walker (shoulder) face late fitness tests, but Wales pair Sonny Parker (knee) and Jonathan Thomas (shoulder) are sidelined, although they hope to be fit for next week's Edgeley Park encounter against Sale.