Ireland centre Luke Fitzgerald has been ruled out of Saturday's Test against New Zealand in Wellington with an ankle injury.
The Ireland management team had been confident the 20-year-old, who missed the first two days of training in Wellington, would be fit in time for Thursday's training session but he has now failed a fitness test.
"The injury didn't respond as quickly to treatment as our medical team had predicted," team manager Joey Miles said. "However, we're still reasonably optimistic Luke will be available for the Test in Australia."
It means Ireland fans must wait a little longer to see captain Brian O'Driscoll and Fitzgerald in the midfield. The Leinster team-mates had also been due to combine against the Barbarians before O'Driscoll left the camp following the death of a close friend.
Ulster's Paddy Wallace will step in, while Leicester's Geordan Murphy moves onto the bench.
While disappointed for Fitzgerald, Miles said the Irish were not unduly concerned about having to make the change with just over 48 hours to the match.
"Paddy Wallace has a pedigree of playing inside centre with his club Ulster," added Miles. "We knew there was an outside possibility of this happening so Paddy Wallace has trained most of the week in that position."
New Zealand's explosive inside centre Ma'a Nonu, in particular, is expected to attack that midfield channel, and how the 81-kilogram Wallace contains those forays will be crucial.
"Anyone who plays at inside centre in international football has got to expect that type of challenge. Paddy is more than up to it," said Miles.
But defence coach Graham Steadman said it was not just Nonu the Irish had to be wary of.
"What we've got to do is trust our defensive system," he said. "The All Blacks will pose problems all over the park if they're given time and space to execute. What we've got to do is cut down on space."
One factor that could work in Ireland's favour will be the fact the match will be played under the laws used during the northern hemisphere season.
The Super 14 competition was played under the Experimental Law Variations this year but New Zealand have been keen to play down the impact of reverting to a different set of rules in the space of a week.
"We're just looking at it positively and taking what we can from the ELVs and the game that it produced and trying to apply that in the game we've got on Saturday," All Blacks assistant coach Wayne Smith said.
"We're not looking at it as old laws and new laws we're looking at is as our laws and our game and how we want to play and hopefully that will be all right."
The 2017 RBS 6 Nations was watched by record numbers of fans
29 March 2017, 12:25pm
After an enthralling RBS 6 Nations Championship of twists, turns, and no small amount of drama on the last day, figures show the RBS 6 Nations is going from strength to strength, year on year, with no sign of slowing down.