Ireland back row Caelan Doris and lock Quinn Roux will not play a part in Sunday's Six Nations opener against Wales due to injuries and have returned to their provinces for medical assessment, the country's rugby union (IRFU) said.
Doris, who made his Ireland debut at last year's Six Nations, has seven caps and was expected to start against Wales while Roux has played 16 times for his country.
"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," IRFU said in a statement on Tuesday.
"Quinn has a neck complaint that has not settled so he has returned to Connacht."
The IRFU added that Munster back row Gavin Coombes and Leinster lock Ryan Baird would train with the squad this week ahead of Sunday's game in Cardiff.
No other injuries were reported and skipper Johnny Sexton is expected to be named in the squad on Friday despite picking up a muscle injury in Leinster's win over Munster last month.
Ireland, who last won the Six Nations in 2018, finished third last year after losses to England and France.