Leinster captain Isa Nacewa will miss the Pro12 final after damaging a metal plate in his arm from an old injury.
The 33-year-old came out of retirement to return for his second stint at Leinster this term, but will now miss Saturday's showdown with Connacht at Murrayfield.
Rob Kearney's return from a two-week ankle injury could not have proved more timely then, with the Ireland full-back proving a straight replacement for Nacewa.
Former Auckland Blues full-back Nacewa aggravated an old arm problem in Leinster's 30-18 semi-final victory over Ulster and, despite early hopes he could ride out the issue, has since been ruled out of action.
"Captain Isa Nacewa has been ruled out with an arm injury suffered in the game against Ulster," Leinster confirmed in a statement.
"While that injury came back clear from the initial X-ray, a subsequent scan on Monday showed damage had been done to an older injury and in particular to one of the screws that he has in the plate in his arm, which affected his ability to grip.
"As a result, Jamie Heaslip, the vice-captain, will lead the team."
Ireland lock Devin Toner is absent for personal reasons, leaving Ross Molony and Mick Kearney an inexperienced second row pairing.
England call-up Ben Te'o will play his last game for Leinster before his summer switch to Worcester, partnering Garry Ringrose at centre.
Connacht boss Pat Lam has by contrast named an unchanged match-day squad for the first time all season, ahead of the province's maiden Pro12 final.
Galway native John Muldoon will captain the province in his 275th appearance, while Ireland prop Finlay Bealham remains Connacht's sole ever-present star this term.
Ireland centre Robbie Henshaw will play his final game for Connacht in Edinburgh this weekend, with the chance to deny his future club Leinster some silverware.
"It's exciting that this is the first time in 31 games that we've been able to name the same match-day squad from one week to the next," said Connacht boss Lam.
"These 23 players are the fortunate ones who have earned the opportunity to wear the jersey and represent their team-mates and the whole of Connacht in our first final.
"Preparation continues to be our big focus this week. We know how tough it will be against Leinster, who have a huge amount of experience in finals rugby.
"But we know that if we stick to our structures and systems and channel all the emotion and physicality into our performance, we have a real chance of making history."
Source: PA
