Loss of Ryan can take heat out of engine room
The omission of Donnacha Ryan could make all the difference to the outcome in Murrayfield.
This is not to take away from the special qualities Iain Henderson will bring to a typical Six Nations arm wrestle.
It is just with Seán O'Brien, CJ Stander, Jamie Heaslip and the new bump of Jack McGrath and grind of Tadhg Furlong Ireland have enough ball-carriers.
What they are slightly short on is lineout leadership from the loss of Peter O'Mahony and the good old fashioned grit Ryan has been showing in Munster's season.
For all the garlands hung around the necks of Stander and Conor Murray, it has been Ryan's heartbeat that has pulsed through every major Munster performance.
The retirement of Paul O'Connell and move away of Donncha O'Callaghan has finally given Ryan the room to show what he has deep inside of him.
"He had a niggling medial ligament so he didn't train last week," Joe Schmidt said of the Munster man.
"Tuesday was the first time he trained. He's been super for us in recent times but it really is a tight turnaround and we just had uncertainty around Donnacha.
"We wanted to see how he finished up after training on Tuesday and he came through really well, trained well today as well.
"But, we wanted more certainty than that and at the same time Iain has done a super job for us in the past and Dev' (Devin Toner) has also given us sterling service," added Ireland's head coach.
The heavier set Henderson has the bulk, light footwork and freakish natural power to trade blow-for-blow with the Gray Brothers, Richie and Jonny.
It is when the ball is hidden somewhere in the deep, dark trenches that Ryan comes into his own.
What Ireland also need is an alternative ball-winner to Devin Toner. This is where Ryan and Peter O'Mahony would have come in handy.
"We have looked at them in a fair bit of depth there," said Henderson.
"We know they put pressure on.
"They are probably one of the better contesting teams in the Six Nations," added the Ulster man.
"We know we have to knuckle down, get our own detail right, concentrate on ourselves, make sure we do what we know we can do right."
The considerable carrot is there for Henderson to take the shirt against teh Scots and keep it.
- Scotland v Ireland, tomorrow (KO 2.25, live RTE2)