Luke Fitzgerald's hopes of featuring in Ireland's Six Nations opener against Wales appear over after he was ruled out of the Irish Wolfhounds squad for Saturday's game against England Saxons.
The Leinster wing continues to be troubled by hip and neck injuries.
Munster's Simon Zebo has therefore been called up to the Wolfhounds squad.
Jack McGrath, Fionn Carr and Ulster's Craig Gilroy have been drafted into the group of young players who will train with the Ireland squad this week.
Zebo, who scored a hat-trick of tries in Munster's Heineken Cup win over Northampton on Saturday, was supposed to be in the group of six players gaining experience which also included Ulster prop Paddy McAllister and Leinster's Andrew Conway.
Conway and McAllister have been forced to pull out of the training camp because of injury.
There were no uncapped players in the main 24-man Irish squad, with the six additional "up and coming players" set to gain further experience by training with the senior squad for a week prior to the Wales game in Dublin on 5 February.
Ireland coach Declan Kidney has stayed loyal to the men - including Gordon D'Arcy, Paddy Wallace and Eoin Reddan - that played at the World Cup, with scrum-halves Isaac Boss and Tomas O'Leary named in the second-string Wolfhounds panel.
However, Kidney has emphasised that Wolfhounds could still be promoted to the senior squad.
Leinster lock Leo Cullen is an injury doubt with an Achilles injury, but he has been named in the senior squad.
With Brian O'Driscoll ruled out of the Six Nations by a shoulder injury, Paul O'Connell will captain the Irish team.
Ireland squad (24): Rory Best (Ulster), Tommy Bowe (Ospreys), Tom Court (Ulster), Sean Cronin (Leinster), Leo Cullen (Leinster), Gordon D'Arcy (Leinster), Keith Earls (Munster), Stephen Ferris (Ulster), Cian Healy (Leinster), Jamie Heaslip (Leinster), Shane Jennings (Leinster), Rob Kearney (Leinster), Fergus McFadden (Leinster), Conor Murray (Munster), Sean O'Brien (Leinster), Donncha O'Callaghan (Munster), Paul O'Connell (Munster), Ronan O'Gara (Munster), Eoin Reddan (Leinster), Mike Ross (Leinster), Donnacha Ryan (Munster), Jonathan Sexton (Leinster), Andrew Trimble (Ulster), Paddy Wallace (Ulster)
Additional players (6): Fionn Carr (Leinster), Craig Gilroy (Ulster), Jack McGrath (Leinster), Ian Nagle (Munster), Peter O'Mahoney (Munster), Tiernan O'Halloran (Connacht)
Wolfhounds squad (22): Stephen Archer (Munster), Isaac Boss (Leinster), Gavin Duffy (Connacht), Chris Henry (Ulster), Denis Hurley (Munster), David Kearney (Leinster), Ian Keatley (Munster), Ronan Loughney (Connacht), Ian Madigan (Leinster), Mike McCarthy (Connacht), Kevin McLaughlin (Leinster), John Muldoon (Connacht), Tomas O'Leary (Munster), Eoin O'Malley (Leinster), Rhys Ruddock (Leinster), Mike Sherry (Munster), Nevin Spence (Ulster), Devin Toner (Leinster), Dan Tuohy (Ulster), Damien Varley (Munster), Brett Wilkinson (Connacht), Simon Zebo (Munster).
Not considered due to injury:
Brian O'Driscoll, David Wallace, Darren Cave, Felix Jones, Jerry Flannery, Eoin Griffen*, Denis Leamy, Niall Ronan.