Jonathan Sexton has been ruled out of this weekend's final Six Nations clash against Italy after tearing a tendon in his left foot.
Sexton had recovered from the hamstring injury that kept him out of the Scotland and France games and was initially named at fly-half for the match at the Stadio Olimpico.
However, this afternoon the IRFU said he had injured his foot in training and confirmed that he would miss the match against Italy.
Paddy Jackson will now start at outhalf - Ian Madigan joins the replacements.
The game against Italy will see Brian O'Driscoll play what could be his final Six Nations match.
He was included in Ireland's starting XV despite suffering concussion during last weekend's 13-13 draw with France.
Luke Marshall was also concussed during the game - but both players have been passed fit for the trip to Rome on Saturday.
Ireland XV to play Italy: Rob Kearney, Craig Gilroy, Brian O'Driscoll, Luke Marshall, Keith Earls, Paddy Jackson, Conor Murray; Cian Healy, Rory Best, Mike Ross, Mike McCarthy, Donnacha Ryan, Peter O'Mahony, Sean O'Brien, James Heaslip.
Replacements: Sean Cronin, David Kilcoyne, Stephen Archer, Devin Toner, Iain Henderson, Paul Marshall, Ian Madigan, Luke Fitzgerald.
In other team news, Craig Gilroy returns on the right wing after overcoming a groin strain, replacing rib-fracture victim Fergus McFadden.
The pack is unchanged from the eight that started against France with lock Donnacha Ryan being given a clean bill of health after taking a bang on his shoulder at the Aviva Stadium on Saturday.
Substitute scrum-half Eoin Reddan fractured his leg against France, so uncapped Ulsterman Paul Marshall wins a spot on the bench that includes Devin Toner.
Kidney explained that Toner's line-out prowess earned him the nod over Donncha O'Callaghan as second row cover.
Ireland have never lost to Italy in the Six Nations with their last defeat to the Azzurri coming in 1997.
Victory in Rome, combined with France dispatching Scotland in Paris, would secure a third-place finish - a reasonable return given the number of injuries they have endured in the championship.
But defeat, also combined with a French win, would thrust them into contention for the wooden spoon.