Leinster and Ireland hooker Richardt Strauss will miss the entire Six Nations.
The 26-year-old, who made his Ireland debut last November, has an ankle injury and joins Ulster's Roger Wilson, who was considered, but has been ruled out with a hamstring injury.
Ireland head coach Declan Kidney has added seven players to the training panel.
Munster's James Coughlan, Tommy O'Donnell, Mike Sherry, Damien Varley and Ian Keatley have been added along with Leinster's Rhys Ruddock and Kevin McLaughlin.