Ireland forwards Caelan Doris and Quinn Roux look certain to miss the Guinness Six Nations opener against Wales after returning to their provinces for medical assessment.
Leinster number eight Doris, who was arguably his country's standout performer during the Autumn Nations Cup, has symptoms of concussion.
South Africa-born lock Roux has a neck complaint and rejoined Connacht.
Munster backrow Gavin Coombes and Leinster lock Ryan Baird will train with Andy Farrell's side this week, ahead of Sunday's meeting with Wayne Pivac's men in Cardiff.
Captain Johnny Sexton, forwards Iain Henderson, Tadhg Furlong and Peter O'Mahony and winger James Lowe were among the injury doubts included in head coach Farrell's initial 36-man selection.
According to a statement from the Irish Rugby Football Union, all players still in the camp are expected to train this week.
