Mayo native Caelan Doris is set to miss out on Ireland’s Six Nations opener against Wales.
The Lacken man and Connacht’s Quinn Roux are both ruled out through injury.
Doris has flagged some symptoms that the IRFU claim "could be associated with concussion".
He has returned to Leinster to allow his symptoms to be appropriately assessed and investigated.
Roux has a neck complaint that has not settled and will go back to Connacht.
Munster backrow Gavin Coombes and Leinster lock Ryan Baird have been called up to the squad.
All other squad members are expected to train this week ahead of the opening Guinness Six Nations clash with Wales on Sunday.