Caelan Doris and Quinn Roux have both been ruled out of Ireland's Six Nations opener against Wales in Cardiff this Sunday.
Head coach Andy Farrell has drafted in uncapped pair Ryan Baird and Gavin Coombes to replace the injured duo.
It's Baird's second time being called-up to the squad; the versatile Leinster second and back row was part of the squad that trained during the 2020 Six Nations this time last year, but was injured by the time the tournament resumed in the Autumn.
Coombes, meanwhile, has been a revelation at both blindside flanker and number 8 for Munster this season, forcing his way past Jack O'Donoghue in the pecking order as a first choice in the backrow.
The IRFU confirmed that Doris and Roux will both be returning to their provinces for medical treatment, with Caelan Doris experiencing concussive symptoms, and Roux dealing with an ongoing neck problem.
"Caelan has flagged some symptoms that could be associated with concussion. He has returned to Leinster to allow his symptoms to be appropriately assessed and investigated.
"Quinn has a neck complaint that has not settled so he has returned to Connacht.
"Munster backrow Gavin Coombes and Leinster lock Ryan Baird will train with the Ireland squad this week.
"All other squad members are expected to train this week," their update concludes, indicating that Johnny Sexton should be fit and ready following his hamstring scare.
CJ Stander now seems likely to start at number 8 for Ireland this Sunday, with the rest of the backrow options seemingly wide open.
Many had expected Peter O'Mahony to get the nod at openside flanker, where he has played regularly for both club and country this season, but he could now be switched back to his more familiar role of 6, with one of Will Connors or Josh van Der Flier slotting in at openside.
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