Andew Omobamidele has emerged as a doubt for the World Cup qualifier with Portugal.
The Norwich City defender requires further assessment after suffering an Achilles problem in Saturday's 2-1 win away to Brentford. Omobamidele played the full 90-minutes of the game at the Brentford Community Stadium.
Meanwhile, Jayson Molumby is definitely out of Thursday's game at the Aviva. The on-loan West Brom midfielder has a hamstring injury.
Omobamidele's absence would be a huge blow for Stephen Kenny, however. He's blossomed on the international stage, having made his debut as a substitute for Dara O'Shea in September's heartbreaking 2-1 defeat in Faro.
He's played every single minute of Ireland's last three games and - if fit - would be a certain starter against Portugal.
On Wednesday evening, Kenny said that Burnley's Nathan Collins would be next in line to slot into the defensive unit, should Omobamidele miss out.
"Yeah, Nathan has done very well," said the manager, "And he's certainly in contention, that's for sure.
"It's an area that, I really think that three emerging players coming through in that position... is great for our future really. With Dara O'Shea (who got injured in Faro), Nathan Collins and Andrew Omobamidele who's been absolutely excellent for us so far, since he made his debut.
"[He's] looked so natural at this level, and it's been great to see."
Thursday's visitors aren't without selection issues of their own. Bernardo Silva misses the trip to Dublin with a muscle injury.
Meanwhile, Portugal head coach Fernando Santos will spend Thursday's game on tenterhooks, as six of his players are a booking away from missing their showdown with Serbia on Sunday.