Lions legend Gareth Edwards has predicted "a very close call" between flankers Martyn Williams and David Wallace to face South Africa in Saturday's first Test.
Head coach Ian McGeechan will name his line-up for the ABSA Stadium showdown tomorrow.
And while the side looks to be largely cut and dried, Wales veteran Williams could yet mount a late challenge to Munster openside Wallace.
"It will be a very close call between them," claimed former Wales and Lions scrum-half Edwards.
"There could even be a case made for them both playing."
Were McGeechan to go down that route, then either prospective blindside Tom Croft or number eight Jamie Heaslip - positions Wallace can both play in - might miss out.
Elsewhere though, Edwards - a victorious 1974 Lion in South Africa - believes McGeechan is unlikely to contemplate any surprise selection calls.
"I expect Brian O'Driscoll and Jamie Roberts to be the centres - they've been terrific together on this tour - and I expect to see Gethin Jenkins at loosehead prop, with Ugo Monye on the left wing."
The Lions have reeled off six successive wins on the way towards an eagerly-awaited opening Springboks showdown.
But the tour's business end is about to commence, with recent history suggesting the Lions are up against it, having gone six games without a Test win stretching back to when they beat Australia in Brisbane eight years ago.
Edwards added: "The Lions will be so proud to be unbeaten on this tour, but they will also be aware they haven't reached their best.
"There have been a couple of games so far when it could have gone either way, but the reality now is they know they have to raise the bar.
"I remember the 1968 South Africa tour. We only lost one provincial match to a very good Transvaal team, but when it came to the Tests, we lost 3-0, with one draw.
"It's only the Tests that matter - they are what make that mark in the sand.
"A lot is said about the Springboks perhaps being undercooked (they haven't played a Test since November). By contrast, the Lions have been building up intensity.
"At some point, someone will take control of a moment in the game that makes a difference - someone will have that effect on the game."
Eddie Jones has announced his 27-man squad to train in Oxford until Friday March 3 with centre Jonathan Joseph recalled to training after being released back to Bath during England's win over Italy in Round Three of the RBS 6 Nations.