Stephen Ferris insists Ireland must use the New Zealand tour to find the new Johnny Sexton - even if there is no clear candidate right now.
Ferris can understand that Sexton, who turns 37 ahead of the third Test against the All Blacks, will want to start all three internationals next month.
But the ex-Ulster and Ireland ace wants Andy Farrell to give opportunities to who he believes could replace Sexton if things go pear-shaped before or during next year's World Cup.
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Ferris said: "It still baffles me that everyone is still hanging their hat on Johnny Sexton being fit for a World Cup in 2023 and if Ireland don't have Johnny Sexton for that, then they're never going to win it.
"That's how everybody feels.
"Johnny's the captain, he's going to want to make history, to have another column on his Wikipedia page that says 'beat the All Blacks out there' - and if I was in his shoes I'd be thinking exactly the same.
"How he goes about his duties for the younger lads, that's brilliant. Him being out there is definitely justified.
"I don't think he needs to play all three Tests. Some of the other lads do - they need minutes at a high level against arguably the best side in the world.
"But I don't think leaving at home, wrapping him in cotton wool is going to ensure that he's fit for a Rugby World Cup in 2023.
"His hunger for work and to be the best he can be is always going to drive him on and if he thinks he's fit and ready, he'll be banging on Andy Farrell's door to play all three Test matches."
However Ferris claims it is a "big call" for Farrell to gamble on Sexton being fit and in top form in the finals in France.
He urged: "You've got to have other people who are ready to perform at the elite level.
"So maybe it's the perfect opportunity not to play Johnny in any of the Test matches and see what the other guys are like.
"If Johnny plays in all three Tests, before you know it you're into the Autumn internationals and the World Cup is less than a year away and you're still asking the question, who's going to be the next Johnny Sexton?
"If we don't find that out in the next five weeks, then you're hanging your hat on Johnny Sexton for the World Cup."
Ferris accepts that there is no clear answer as to who could replace Sexton.
He references the lack of game time Leinster pair Harry Byrne and Ciaran Frawley have had at out-half this season.
Joey Carbery is second in the pecking order but Ferris is concerned, pointing to the "absolute shocker" the Munster star had in the URC quarter-final loss to Ulster.
"He went into his shell in a big game, he missed touch with penalties, skewing the ball off the outside of his boot. His game management was very poor," recalled Ferris.
"He runs sideways a lot with the ball whereas you look at the way Johnny attacks the line, he’s so square on, he gives the boys outside him more time on the ball.
"If Harry Byrne is going to be that guy, surely he’s going to have to start some Test matches.
"We’re running out of time before the World Cup, it’s going to be upon us in no time.
"The likes of Harry or Joey have got to get more game time in a green jersey with a no 10 on their back, not no 23."
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