Three into two might work out for McCarthy
It remains to be seen who will be biggest loser in the 'three overseas players into two won't go' rule that must be factored into Leinster's European Cup and PRO14 League campaigns.
The Cotonou Trade Agreement, formulated in 2000, allows European clubs to play as many South Africans and South Sea Islanders as they want.
While, it prevents them from going for more than a combined total of two representatives from Australia and New Zealand.
It looks like Scott Fardy is a nailed on certainty for The Champions Cup quarter-final against Saracens.
All things being equal and all players being free from injury, it then becomes a two-man race between scrum-half Jamison Gibson-Park and left wing James Lowe.
There is no shortage of potential wingers on the roster between Fergus McFadden, Jordan Larmour, Dave Kearney, Adam Byrne and Barry Daly.
Rightly or wrongly, the choice between the two New Zealanders will just boil down to playing resources.
It could all swing on whether scrum-half Nick McCarthy can convince coaches Leo Cullen and Stuart Lancaster if he has what it takes to man the bench against the champions at Lansdowne Road on April 1.
Of course, the current knee injury to Luke McGrath could become a factor.
The most recent update rated the number nine as certain to be ready for Saracens.
These medical calculations have a way of meeting with setbacks when markers are not met.
"Being realistic, it will lead to more opportunities for me, in terms of game-time," said McCarthy.
"But, I also have to worry about my own stuff, working hard at training every week and getting better and putting my best foot forward,
"If I play well, hopefully, I'll get picked on merit as opposed to getting in on the rule."
The former Ireland U20 captain has been expanding his experience this season.
There have been thirteen caps since September, his first start coming in a two-try salvo against Southern Kings.
McCarthy, just 22, is busy building the caps and the confidence to challenge the supremacy of Gibson-Park and McGrath.
"You have to just back your own ability," he said.
"You probably wouldn't be around this environment if you didn't.
"It is really important that you do that."