Joe Schmidt has admitted Garry Ringrose was a "needs-must" selection for Ireland's crucial NatWest 6 Nations clash with Scotland.
Ringrose has just an hour's rugby with Leinster under his belt since an ankle problem in January, but must now act as the cure to Ireland's injury-hit midfield.
The 23-year-old will start at outside centre on Saturday, in the absence of long-term injured trio Jared Payne, Robbie Henshaw and Chris Farrell.
Head coach Schmidt conceded doubts remain over Ringrose's ability to last the full 80 minutes, with replacement Jordan Larmour or wing Keith Earls the next options to deputise at centre.
"There's always concerns about players for different reasons, and Garry's only had six games in this entire season," said Schmidt, of Ringrose.
"That's something you calculate in but sometimes you don't have the luxury of a plethora of options.
"Garry's been extraordinary when he has played for us, he's done great.
"We're hoping he can hit the ground running and get straight back into that form.
"He's a smart player, and hopefully he can get the balance between when he has to work hard and when he can get a breather back on the pitch.
Ulster centre Payne has not played since last summer's Lions tour to New Zealand, having suffered persistent headaches.
Leinster star Henshaw dislocated his right shoulder in Ireland's 56-19 win over Italy in Dublin, and Munster's Farrell tore knee ligaments in training.
Quick-witted centre Ringrose therefore becomes the third man to wear Ireland's 13 shirt in this year's Six Nations.
Lions duo Tadhg Furlong and Iain Henderson return after hamstring problems - though Henderson only to the bench, with youngster James Ryan partnering Devin Toner at lock.
Henderson had been widely tipped to slot straight back into the starting line-up, but Schmidt has kept faith with his most-selected player in Toner.
The 31-year-old will this weekend make his 44th Ireland start under Schmidt, in the Kiwi coach's 54th match at the helm.
Pivotal half-backs Conor Murray and Johnny Sexton have also shrugged off knocks in time for Saturday's Aviva Stadium showdown, as Ireland hunt a fourth-straight win in this year's competition.
Beat Scotland this weekend and Ireland would then face England at Twickenham on Saturday, March 17 chasing a first Grand Slam in nine years.
Ireland boss Schmidt insisted he has full faith in Lions fly-half Sexton's readiness to kick at goal, after a back issue had hampered his performance off the tee in the 37-27 win over Wales two weeks ago.
Sexton missed 10 points with the boot in an unusually off-kilter kicking showing, but Schmidt insisted the Leinster star is now back to full fitness, and sharpness.
"I'm super confident, he's a world-class kicker," said Schmidt, when asked to assess Sexton's fitness.
"I would have no hesitation in Johnny making any decision about any kick he'd have.
"I think he actually struck three of those four kicks quite well against Wales. I don't think he was a million miles away."