Chris Henry is likely to miss the rest of Ireland's Six Nations campaign after damaging knee ligaments.
The flanker was hurt during Ulster's RaboDirect Pro 12 game against Zebre on Friday, and the Irish RFU confirmed the injury will require surgery.
Henry has initially been pulled out of the squad to take on Scotland on Sunday, but an estimated four-week rehabilitation period means his Six Nations is almost certainly over.
Munster back row Tommy O'Donnell has been called up as cover for Henry, who came off the bench in both the victory in Wales and the home defeat to England.
Ian Madigan is in for injured Connacht centre Dave McSharry, who has a groin problem.
Revised Ireland squad: Best, cave, Court, Cronin, Coughlan, Earls, Fitzgerald, Fitzpatrick, Gilroy, Henshaw, Heaslip, Henderson, Jackson, Kearney, Kilcoyne, Madigan, Marshall, McFadden, Murray, O'Brien, O'Donnell, O'Driscoll, O'Gara, O'Mahony, Reddan, Ross, Ryan, Stevenson, Toner.