Joey Carbery has suffered a suspected broken arm and will play no part in Ireland’s final autumn international against Argentina on 25 November.
The Leinster playmaker picked up the injury in the second half of Ireland’s over Fiji in Dublin.
“I think he’s fractured his left forearm,” confirmed head coach Joe Schmidt, who reported no other injury concerns after Saturday’s poor display.
“That will mean he won’t take any further part in the series for us.”
Ireland squandered a 17-3 lead built up by tries from Darren Sweetnam, Dave Kearney and Jack Conan, and failed to score for 32 minutes as Fiji drew level five minutes into the second half.
Carbery’s two missed conversions looked like potentially costly errors before replacement Ian Keatley’s two late penalties squeezed Schmidt’s inexperienced side home.
Ireland made 13 changes from last weekend’s record over South Africa, and endured some nervy moments with Henry Seniloli and Timoci Nagusa claiming tries for Fiji, with Ben Volavola slotting 10 points from the tee.
Schmidt was relieved, but also praised Carbery’s performance on just his second start in six caps.
“Joey was a bit special, the way he cut the line and got that pass into the hands of Darren Sweetnam, who finished comfortably for the try,” he said.
“I thought Joey’s ability to organise others is coming along; his vision is really good.
“The threat he poses at the line himself, he ducked and dived, but he’s brave, potentially to a fault. He pays no heed as to what’s in front of him.”
Natural successor to Sexton’s 10 jersey
Schmidt insisted Ireland must accept Leinster’s need to deploy both Carbery and British and Irish Lions star Johnny Sexton in their starting line-up, even if it denies the youngster regular opportunities at fly-half.
“Look, it is what it is, it’s an unfortunate situation for us, but I totally understand it,” said Schmidt, of Leinster regularly fielding Carbery at full-back.
“They’ve got Johnny Sexton at Leinster, so Joey takes his opportunities at full-back.
“I just appreciate that he gets game time and is in good condition to play.
“I’d love him to play 10 more often, it would help his development, but it’s a needs-must situation.”
Fiji head coach John McKee admitted his side will leave Dublin frustrated at not winning, having levelled at 17-17 and again at 20-20.
“There’s some frustration for us, we had chances to score another try and secure the win,” said McKee.
“To come back from 17-3 down was a great effort, but maybe that took too much out of us.”