Ulster's Player of the Year Stuart McCloskey and team-mate Will Addison have not been named in Ireland's 44-man training squad for the Rugby World Cup.
Connacht lock Quinn Roux also misses out, although head coach Joe Schmidt has not ruled out further additions to the squad.
There are call-ups for uncapped Munster pair Jean Kleyn and Mike Haley while Leinster's Dave Kearney returns.
Flankers Sean O'Brien and Dan Leavy have been ruled out through injury.
Ireland will play four warm-up matches between 10 August and 7 September before travelling to Japan, where they will face Scotland in their Pool A opener on 22 September.
Utility back Addison, who joined Ulster from Sale last summer, has not featured since January after undergoing a back operation.
The 26-year-old made an impressive start to his Ulster career before making his Ireland debut against Italy in November.
"Some players have missed out through injury and there are one or two guys that may be added into the squad at a later stage," said Schmidt on Tuesday.
"There were some very close calls in selection and it's always a challenging process because the coaching group are very conscious of how hard the players work."
Addison's Ulster teammate McCloskey misses out despite enjoying an impressive campaign which earned him a place in the Pro14 dream team.
The centre, 26, has found his international opportunities limited since debuting against England in 2016 largely due to the ferocious competition for places in Ireland's midfield.
South Africa-born lock Kleyn is eligible for selection through the three-year residency rule having joined Munster in 2016.
His provincial teammate Haley has impressed since arriving at Thomond Park from Sale last summer and will hope to make his Irish debut in the team's summer fixtures, which begin at home to Italy.
Ireland training squad
Forwards: Finlay Bealham (Connacht), Rory Best (Ulster), Tadhg Beirne (Munster), Jack Conan (Leinster), Sean Cronin (Leinster), Ultan Dillane (Connacht), Tadhg Furlong (Leinster), Cian Healy (Leinster), Iain Henderson (Ulster), Rob Herring (Ulster), Dave Kilcoyne (Munster), Jean Kleyn (Munster), Jack McGrath (Leinster), Jordi Murphy (Ulster), Tommy O'Donnell (Munster), Peter O'Mahony (Munster), Andrew Porter (Leinster), Rhys Ruddock (Leinster), James Ryan (Leinster), John Ryan (Munster), Niall Scannell (Munster), CJ Stander (Munster), Devin Toner (Leinster), Josh van der Flier (Leinster).
Backs: Bundee Aki (Connacht), Ross Byrne (Leinster), Joey Carbery (Munster), Jack Carty (Connacht), Andrew Conway (Munster), John Cooney (Ulster), Keith Earls (Munster), Chris Farrell (Munster), Mike Haley (Munster), Henshaw (Leinster), Dave Kearney (Leinster), Rob Kearney (Leinster), Jordan Larmour (Leinster), Kieran Marmion (Connacht), Luke McGrath (Leinster), Conor Murray (Munster), Garry Ringrose (Leinster), Rory Scannell (Munster), Jonathan Sexton (Leinster), Jacob Stockdale (Ulster).