The Lions’ 10-game tour begins on 3 June with the first Test on 24 June in Auckland.
“I know there’s talk at the moment of shortening a Lions tour, but that’s from people who’ve never done it,” McGeechan told the BBC
“The six-game preparation is so important to collective understanding.”
The Lions opening fixture takes place just days after the squad arrives in New Zealand.
And the 10-match schedule has been described as “ludicrous” by leading figures in the English game.
But former centre McGeechan — who played on the Lions’ successful 1974 tour to South Africa and the 1977 loss to New Zealand, before leading four tours as head coach — believes the warm-up games are crucial to Test success.
“A player has to put on a Lions jersey and start with a number on his back in the first three games. He can’t sit on the bench or not be involved,” he said. “You have to wear the number on your back and then you’re a Lion. You’re there in the position you were chosen for.
“There’s the combinations that you need to put together but there’s also that defining element of giving the player the opportunity, and you need all six games.”
In 1974, the Lions travelled to South Africa looking for their first victory over the Springboks in 78 years.
A 27-year-old McGeechan was embarking on his first Lions tour, as a squad of amateurs led by Ireland’s Willie John McBride left home for almost four months.
The tourists played 22 matches between 15 May and 27 July, and won all but the last game, which was a controversial draw — they used just 17 players in the four Tests.
“I always remember when we won the third Test, having won the series in South Africa, Willie John took us all straight to where the mid-weekers were sitting and applauded them.”
“That’s what came over in 1974, the time and effort that was put in by the 13 players who didn’t play Test match rugby over four months.”
Meanwhile uncapped Exeter flanker Don Armand has been named in the England squad for next month’s tour of Argentina. Zimbabwe-born 28-year-old Armand was man of the match as the Chiefs edged Wasps after extra-time in the Aviva Premiership final at Twickenham on Saturday.
Don Armand*, Will Collier*, Ben Curry*, Tom Curry*, Charlie Ewels, Ellis Genge, Dylan Hartley (c), Nathan Hughes, Nick Isiekwe*, Joe Launchbury, Matt Mullan, Chris Robshaw, Nick Schonert*, Tommy Taylor, Sam Underhill*, Harry Williams*, Mark Wilson*
Mike Brown, Danny Care, Joe Cokanasiga*, Ollie Devoto, Nathan Earle*, George Ford, Piers Francis*, Sam James*, Alex Lozowski*, Harry Mallinder*, Jack Maunder*, Jonny May, Henry Slade, Denny Solomona*, Marland Yarde