Ireland boss Schmidt said circumstances led him to pair Robbie Henshaw and Jared Payne in midfield - but challenged the duo to match their physicality with the kind of iron will Brian O'Driscoll and Gordon D'Arcy exuded for a generation.
While D'Arcy has returned to full fitness, Schmidt claimed the Leinster centre had not been ready early enough in the week to complete match-level preparation.
"It was what was available to us at the start of the week," said Schmidt.
"Robbie Henshaw's flexibility to play 12 or 13 is similar to Jared Payne, but that's the way they trained last week, so we've decided to go with that.
"Gordon was injured last week: he's probably back to full fitness now but we weren't absolutely sure of that at the beginning of the week.
"We have very small windows of preparation so we just felt we were partway along a pathway that was looking reasonably positive.
"To be fair to Gordon D'Arcy he has helped immeasurably: he's been a really good mentor for Robbie and Jared this week.
"We thought Gordon would be fit, he probably has made it to be fair to him, but we hadn't had any time with the combinations.
"It was going to be a new pairing no matter what, so we just decided to go with what had been working together.
"To be honest I didn't tell the centres in advance, I just named the team.
"It wasn't too much of a surprise to them because they'd been running in there together.
"I did speak to Gordon beforehand, and he's very much team-orientated as always.
"He's been a massive asset to those two in training.
"Ireland have been blessed with a centre pairing for a huge length of time that have not necessarily been the biggest but been as physical as the best.
"Physicality is sometimes determined by the will rather than the size.
"Hopefully on Saturday we'll get a bit of both from our centre pairing."