Ireland could face a selection crisis at fly-half for their final Test of the year against Australia on Saturday with a doubt over captain Johnny Sexton and his deputy Joey Carbery ruled out.
Irish talisman Sexton has not trained since suffering a dead leg in the 19-16 win over world champions South Africa on November 5.
Carbery has a head injury due to a high tackle early in the second-half of the 35-17 victory over Fiji last Saturday for which Albert Tuisue was sent off.
His Munster team-mate Jack Crowley came on for him in what was his Test debut and is the form horse to step in if Sexton is deemed unfit.
The Irish will also be without centre Robbie Henshaw, who lasted just five minutes against the Fijians before a nagging hamstring injury forced him off.
Either Stuart McCloskey or Bundee Aki -- who has completed a suspension -- are available to replace him.
The Irish will be seeking a 12th successive home win and rubber stamp their number one ranking in the world against a Wallabies side bruised by their defeat at the hands of Italy on Saturday.
"Joey Carbery will complete the return to play protocols at Munster following his removal on Saturday for a HIA," read an Irish Rugby Football Union (IRFU) statement.
"Robbie Henshaw's hamstring issue will rule him out of this week's game against Australia."
They are not the only concerns head coach Andy Farrell has.
Sexton's fellow Leinster team-mates James Ryan, Andrew Porter, Josh van der Flier and Hugo Keenan also picked up knocks in the South Africa match.
"They will be monitored across the early part of the week and re-integrated into training according to their individual management plans," read the statement.