Joe Schmidt has backed rookie playmaker Ross Byrne to seize his World Cup chance in Saturday's clash with England at Twickenham.
Carbery could well miss the World Cup after damaging ankle ligaments in the 29-10 victory over Italy in Dublin on August 10.
— Irish Rugby (@IrishRugby) August 22, 2019
Byrne and replacement Jack Carty can now make their case for World Cup selection at Twickenham, with head coach Schmidt assessing all his fly-half options.
"Ross has trained really well and it's not his debut, he's had time with us before, so we've got a lot of confidence in him anyway and I think he built his way through the season," said Schmidt.
"I thought he was maybe not as impressive as Jack early in the season, and I think those two have become really important to us.
"Joey has done well this week. Johnny, he's fine, but he missed a bit of time with his thumb, so he's a little bit behind and we know how well he plays for us. We don't feel that he needs a lot of time with the experience that he's got.
"So, for us, the guys that need the time are probably Ross and Jack and they've got the opportunity to do that this weekend, that they'll share a bit of time, I'd say, in the middle."
Frontline fly-half Sexton has been recovering from a thumb sprain, and Carbery's ankle injury has whittled down Ireland's playmaking options for their World Cup warm-up encounters.
Schmidt admitted Byrne and Carty's stock has risen markedly in the wake of Carbery's ankle blow.
"They were always really important because it is such a specialist position, but they probably wouldn't have had this opportunity as much," said Schmidt.
"Joey, especially on the back of his 50 minutes against Italy, I thought he was as good as I've seen him.
"I thought he controlled the game really well. He's always a threat individually running and carrying the ball, but I just thought his control of the game was very, very good.
"So, for him, the frustration is not being able to get that opportunity to continue that. It's probably a frustration for us as well, but it's somebody else's opportunity and I know that Ross has trained well this week and is very, very motivated to do the job for us on Saturday."
Asked if Byrne is a more direct replacement for Sexton in style terms, Schmidt continued: "A little bit, that's probably a fair observation.
"I think Ross' ability to control the game, it's one of the things that was defining between Joey and him at Leinster, probably in that Ross ran the game and Joey ran really well individually. But I think it's also something that comes with a rhythm and game time.
"Jack, whenever he came off the bench for us in the Six Nations, I thought he did a super job.
"So we have a lot of confidence in Jack being able to control the game and we do think he can bring a bit of a change up off the bench.
"Either way, I think they'll both get a bit of game time on Saturday to demonstrate what they can bring to the game."
IRELAND TEAM TO FACE ENGLAND AT TWICKENHAM ON SATURDAY: R Kearney, J Larmour, G Ringrose (all Leinster), B Aki (Connacht), J Stockdale (Ulster), R Byrne (Leinster), C Murray (Munster), C Healy (Leinster), R Best (Ulster, capt), T Furlong (Leinster), I Henderson (Ulster), J Kleyn, P O'Mahony (both Munster), J Van Der Flier (Leinster), CJ Stander (Munster). Replacements: S Cronin (Leinster), J McGrath (Ulster), A Porter, D Toner (both Leinster), T Beirne (Munster), L McGrath (Leinster), J Carty (Connacht), A Conway (Munster).