Dan Leavy has been forced to withdraw from Ireland's autumn clash with New Zealand due to "general tightness".
Leavy's Leinster team-mate Josh Van Der Flier will start at openside against the back-to-back world champions in Dublin instead, with Jordi Murphy stepping up to the bench.
An Irish Rugby Football Union (IRFU) spokesman confirmed Leavy had failed a fitness test at Friday's training session.
"Dan Leavy had a fitness test this morning and it was decided he was not 100 per cent, so he will miss the match due to general tightness," an IRFU spokesman confirmed.
Leavy failed to train fully on Thursday due to what head coach Joe Schmidt termed "full-body soreness" after last weekend's 28-17 victory over Argentina in Dublin.
Now the 24-year-old has been withdrawn from Ireland's starting XV for the clash between the world number one side New Zealand and the number two-ranked hosts.
Ireland are understood to have worked through a physical training session on Tuesday, in a bid to steel themselves to face Steve Hansen's gritty All Blacks.
There is no suggestion Tuesday's session contributed to Leavy's injury, but skipper Rory Best admitted the only way to prepare to face New Zealand is to "gear up" physically.
"You know you're going to have to be physical against New Zealand, there's no doubt," said Best.
"New Zealand are renowned for the style of rugby they play, and one to 15 they can all play and put people into space and through holes.
"But probably the area of their game that doesn't get as much credit is their physicality, they are incredibly physical in the tackle area and the carry and at the breakdown.
"So you know that if you don't match that, with the talent they've got across the pitch that it's going to be tough. So you've got to gear up for that.
"And I don't know that necessarily that injuries should be a part and parcel of that.
"Sometimes it happens you could have a week with a short turnaround, where you decided to do no contact and minimise training and someone will still pick something up. That's what happens in professional rugby.
"Against New Zealand you've got to gear yourself up for a physical battle, because it's what they bring."
Leavy had been named in Ireland's starting line-up despite still needing to prove his fitness in Friday's captain's run training session.
Schmidt would usually want all his players fit and training fully on a Thursday at the latest for a Saturday Test match, but had handed Leavy extra latitude.
Now though, with Sean O'Brien already out with a broken arm, Ireland have lost another openside in Leavy, with Van Der Flier stepping up to start.
Best hailed Van Der Flier's quality in stepping up to replace Leavy, with Ireland's impressive depth specifically at openside underscored by the ease of their late changes.
"Someone like Josh, you know he's going to have been diligent regardless of where he's been sat in the squad," said Best.
"He will know his drills inside and out, so from our point of view it doesn't change things massively.
"Because you're replacing a quality player with two more quality players; one to start and one to come onto the bench."