The tourists are in Johannesburg to face namesakes the Xerox Golden Lions some four-and-a-half weeks before they play the last match of the three-Test series against the Springboks in the same city.
McGeechan's men had to come from behind to win their opening match against a Royal XV in Phokeng on Saturday and the head coach and squad members alike know that an improved performance is needed if they wish to remain unbeaten.
Whereas Saturday's opposition came from an amalgamation of five Vodacom Cup sides containing only a handful of players with Super 14 experience, the Golden Lions play their domestic rugby in the southern hemisphere's premier club competition.
They include South African internationals Andre Pretorious and Lawrence Sephaka in the starting XV, with the duo possessing a combined total of more than 50 Springbok caps.
Jano Vermaak, who made his international debut from the bench during Friday night's victory over a Namibian XV starts at No9 for the Golden Lions, while utility back Earl Rose is among the replacements having started for the world champions in their 36-7 win in Windhoek.
Uncapped Saracens-bound hooker Ethienne Reynecke joins Rose on the replacements bench, as does USA Eagles international Todd Clever.
Youngster Louis Ludik may not have appeared for the Springboks just yet, but following a pre-tour injury to Stormers star Conrad Jantjes, the highly-rated full back will be looking to press his claims to fill his country's No15 shirt when the first Test kicks off in Durban on June 20.
Flanker Cobus Grobbelaar captains the side, while, if his performances towards the end of the Super 14 campaign are anything to go by, No8 Willem Alberts possess a major danger from the base of the scrum and in the loose.
The Golden Lions sacked coach Eugene Eloff only last week and placed the experienced Hans Coetzee in temporary charge for the clash with Britain and Ireland's elite.
Coetzee has responded to the challenge by picking a formidable-looking pack, with second rows Willem Stoltz and Brad Mockford standing over two metres tall and fellow lock Franco van der Merwe being moved to the blindside flank from where he will provide an extra threat at the lineout.
With Heineken Cup experience with Agen and European Challenge Cup experience with Petraca under his belt, Stolz could be a key figure this week, while Mockford also has a better understanding than most of the UK game having previously been a member of the London Irish Academy.
The Lions themselves have made no attempt to play down the magnitude of Wednesday's fixture, with McGeechan, tour manager Gerald Davies and match skipper Brian O'Driscoll all aware of the challenge they face at Coca Cola Park.
O'Driscoll skippers the Lions for the fifth time following four appearances as captain on the ill-fated 2005 tour of New Zealand and the 30-year-old will be looking to continue a remarkable season that has so far seen him claim Grand Slam glory with Ireland and Heineken Cup success with Leinster.
O'Driscoll takes over as captain from Paul O'Connell, with the Munsterman rested from the matchday 22 having led the Lions at the Royal Bafokeng Sports Palace at the weekend.
McGeechan makes 12 changes to his starting XV from Saturday's win, with only centre Jamie Roberts, wing Tommy Bowe and back row David Wallace retaining their places.
Wallace moves from No8 to the openside flank, with try-scorer Bowe and the impressive Roberts named on the right wing and at inside centre respectively.
A total of five players who made appearances as replacements against the Royal XV make the step up the starting side, with Mike Phillips, Lee Mears, Phil Vickery and Alun-Wyn Jones replacing Mike Blair, Matthew Rees, Adam Jones and O'Connell, and Jamie Heaslip taking over from Wallace at No8.
A further four players are in line to make their Lions debuts from the start of the match, with six more possible debutant among the replacements.
Rob Kearney, Ugo Monye, Tom Croft and Nathan Hines will all wear Lions colours for the very first time, while Shane Williams is the only substitute with previous Lions experience.
Did you know?
Ugo Monye is the only backline player in the starting line up to play his rugby outside of the Magners League.
What the Lions say:
Lions head coach Ian McGeechan
"If we build on what we did in the second half on Saturday we will do better. We're here as one team, so the team that goes out on Wednesday will take on board what happened on Saturday.
"The team has trained well. We have worked on several key areas following the first match, which has given us a base on which to keep developing our game."
Lions skipper Brian O'Driscoll
" What makes a Lions tour unique is the fact that you have to take your A game to every training session and to every match. I am looking forward to leading the side and looking forward to getting a game under the belt."
"Jamie Roberts had a strong game on Saturday. He's very good going forward with the ball in hand, and I'm looking forward to playing next to him. "