Rhys Ruddock's second broken arm in six months has cost the Leinster flanker a place in Ireland's World Cup squad.
Head coach Joe Schmidt admitted Ruddock would have made his initial World Cup training squad, but for the broken arm sustained while captaining Emerging Ireland against Uruguay.
Munster flyhalf Ian Keatley is a notable absentee from the squad.
Schmidt confirmed Paul O'Connell is the captain of his 45-man training squad, with Ruddock the main casualty.
The 24-year-old missed the RBS 6 Nations after another arm break in European Champions Cup action against Harlequins in December.
"Rhys Ruddock would have been selected but has been ruled out after fracturing his arm against Uruguay last week," said head coach Schmidt.
"The squad selection has been a long process with some very tight decisions.
"Some injured players who are getting close to full fitness have been included while others have missed out due to prolonged absence or lack of opportunity to demonstrate their full Test match readiness."
Ruddock was included in Emerging Ireland's Tbilisi Cup campaign to help boost his match time in readiness for the World Cup training camp.
Instead the Ireland Under-20s graduate must now sit out of the entire build-up and tournament, suffering his latest arm injury in the 33-17 victory over Uruguay.
Leinster's forward duo Jack Conan and Tadhg Furlong are the only uncapped men in Ireland's ranks, as the double Six Nations champions prepare to kick-start their World Cup preparations.
Schmidt's squad will convene at their Carton House base on Sunday night, with four warm-up matches scheduled for August and the first week of September.
The deadline for selecting 31-man World Cup squads is August 31, and Ireland boss Schmidt has already admitted he is finding the final composition of that squad a huge challenge.
Chris Henry has completed his remarkable comeback after suffering a mini-stroke in November to win inclusion in the squad, the Ulster flanker proving himself ready with an impressive showing against the Barbarians last month.
Veteran centre Gordon D'Arcy is among the ranks despite having already played his final game for Leinster, with his full retirement following the World Cup.
Conor Murray and Sean O'Brien had faced minor injuries in the build-up to this initial squad announcement, but both British and Irish Lions are expected to be fully fit well in advance of the August warm-up schedule.
IRELAND Training Squad
Rory Best (Banbridge/Ulster)
Michael Bent (Dublin University/Leinster)
Jack Conan (Old Belvedere/Leinster)*
Sean Cronin (St. Mary's College/Leinster)
Tadhg Furlong (Clontarf/Leinster)*
Cian Healy (Clontarf/Leinster)
Jamie Heaslip (Dublin University/Leinster)
Iain Henderson (Ballynahinch/Ulster)
Chris Henry (Malone/Ulster)
Rob Herring (Ballynahinch/Ulster)
David Kilcoyne (UL Bohemians/Munster)
Jack McGrath (St. Mary's College/Leinster)
Martin Moore (Lansdowne/Leinster)
Jordi Murphy (Lansdowne/Leinster)
Sean O'Brien (UCD/Leinster)
Paul O'Connell (Young Munster/Munster)
Tommy O'Donnell (UL Bohemians/Munster)
Peter O'Mahony (Cork Constitution/Munster)
Mike Ross (Clontarf/Leinster)
Donnacha Ryan (Shannon/Munster)
Richardt Strauss (Old Wesley/Leinster)
Devin Toner (Lansdowne/Leinster)
Dan Tuohy (Ballymena/Ulster)
Isaac Boss (Terenure/Leinster)
Tommy Bowe (Belfast Harlequins/Ulster)
Darren Cave (Belfast Harlequins/Ulster)
Gordon D'Arcy (Lansdowne/Leinster)
Keith Earls (Young Munster/Munster)
Luke Fitzgerald (Blackrock College/Leinster)
Craig Gilroy (Dungannon/Ulster)
Robbie Henshaw (Buccaneers/Connacht)
Paddy Jackson (Dungannon/Ulster)
Felix Jones (Shannon/Munster)
David Kearney (Lansdowne/Leinster)
Rob Kearney (UCD/Leinster)
Ian Madigan (Blackrock College/Leinster)
Kieran Marmion (Corinthians/Connacht)
Fergus McFadden (Old Belvedere/Leinster)
Conor Murray (Garryowen/Munster)
Jared Payne (Ulster)
Eoin Reddan (Lansdowne/Leinster)
Noel Reid (Clontarf/Leinster)
Jonathan Sexton (Racing Metro 92)
Andrew Trimble (Ballymena/Ulster)
Simon Zebo (Cork Con/Munster)
*Denotes uncapped player