Head coach Sir Clive Woodward will unveil his Test line-up on Wednesday, but the task now for non-Test team coaches McGeechan and Gareth Jenkins revolves around keeping those selected for Tuesday's trip to Invercargill upbeat.
Welsh scrum-half Gareth Cooper makes his first tour start on Tuesday, while the likes of wing Mark Cueto, hooker Andy Titterrell and prop John Hayes appear some way off Test contention.
But Gavin Henson, flanker Martyn Williams and full-back Geordan Murphy are certain to feel acute disappointment, given that they held realistic Test ambitions before leaving Heathrow almost four weeks ago.
"We are talking about established international players, and there will be disappointments this week," said McGeechan.
"But you have got to remember that around 50 per cent of Lions players not selected in the first Test, play Test rugby at some stage in a Test series."
Welsh back-row forward Ryan Jones' reward for a blistering Lions debut against Otago yesterday has been recognised with a likely place on the Test bench.
Yet his fellow warriors at the 'House of Pain' - fly-half Charlie Hodgson and flanker Simon Easterby - have missed out.
Lewis Moody, though, will look to get his tour back on track after seeing it severely disrupted by a knee injury which forced him out of the last two games.
For his part, Woodward is relishing the build-up this week, acknowledging that the Lions' travelling fans will turn Christchurch into a sea of red.
"I am very confident with this group of players, and the Test series will be won or lost by 45 players," he said.
"How the non-Test 22 react this week will be very important. Just because you are not picked this week, there are still two Tests to go and there is time for players to come through."