Bernard Jackman predicts the Autumn series represents the last chance saloon for World Cup hopefuls to claim their ticket to France 2023.
Andy Farrell could name his squad today for the clash with South Africa on November 5 - the first of three Tests that Ireland will play next month at the Aviva Stadium with Fiji (November 12) and Australia (November 19) to follow.
France and England have named eight and five uncapped players in their respective squads for their Autumn games.
READ MORE: All bets off as Leinster and Munster collide but Andy Farrell faces anxious wait
But Jackman, the ex-hooker and coach turned pundit, believes that opportunities will be limited for World Cup bolters to stake their claim.
"This November is key," said Jackman, speaking on a media call for the BKT United Rugby Championship.
"If they don't get in this November and get meaningful game time, I think they'll struggle.
"The likes of Rob Baloucoune, he has something to offer, but he would have been better off playing URC than down on the Emerging Ireland tour.
"If Faz has seen something over the last year where he wanted to give those guys game time and couldn't, now he's going to say, 'I need to find out by November'."
Jackman points to the talent reserves Eddie Jones and Fabien Galthié have across more clubs in England and France.
But he was surprised that Galthié made so many changes.
"I would have thought France were more settled off the back of a successful two seasons," he remarked.
"But Galthié sees this as his last chance, too, to look at people. If the new ones don't feature or perform, then he'll go back to what he knows.
"Ireland is a bit more conservative. That's probably down to our player pool and central contracting. We know what's out there."
Farrell's hopes of watching Munster's Craig Casey against URC leaders Leinster at the Aviva Stadium on Saturday appear to be scuppered.
Casey and Tadhg Beirne are to be scanned after suffering groin injuries in Munster's victory over the Bulls and could spell bad news for them facing the Springboks.
For Jackman, scrum-half is a problem area, with first-choice Jamison Gibson-Park dealing with a calf injury.
"He's key to Ireland at the moment," he said.
"His introduction and becoming a starter ahead of Conor Murray has been very much aligned to how we want to play and it's massive to Ireland that he's fit.
"If he's not, Craig Casey is a like for like type of player.
"Conor Murray is obviously centrally contracted and has been on the bench to close out games.
"I don't think you can start Conor Murray against the Boks if you want to play that high tempo game.
"You'd be looking for Casey to show he's the number one in Munster - and maybe he would be the guy to start against the Boks.
"I don't think there's anyone who is going to come from nowhere to feature against the Boks or Australia, but maybe the likes of Thomas Ahern or Jack Crowley could feature against Fiji.
"It takes a bit of time to move up the pecking order because results have been good at international level.
"When they're good, there's no need to change."
Jackman added: "Us going to New Zealand and beating the All Blacks, even if they might have been in a bit of transition, was a massive step forward for us.
"We know that open, high tempo game that Farrell has been trying to implement can work.
"The question is, can it work against the Boks? Can it work against England or France, who are more powerful than the rest and that's where they base their game?
"The best test we're going to get is against the Boks."
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