Kevin Foley became the second man to be ruled out of Ireland’s Euro 2012 squad after failing to recover from a hamstring injury.
The Wolves defender will miss out with Paul McShane coming in to make up the nation’s 23-man squad.
Foley joins Keith Fahey on the sidelines after the Birmingham man was sent home at the weekend.
Trapattoni admitted giving the player the news was tough. He said: "Although Kevin has been recovering well, I have made the difficult decision to leave him out of the 23-player list after completing fitness tests on John O'Shea and Paul McShane this morning.
"I have spoken to him and understand how difficult it is, saying that he can remain with the squad if he wishes."
The Irish are currently in Italy preparing for the championships after beating Bosnia-Herzegovina on Saturday.
However the veteran coach’s job has been made harder by a succession of injuries with goalkeeper Shay Given and defender John O’Shea still nursing knocks.
Trapattoni said: "With the injuries that we experienced in the squad over the past week, I have had to make a tough decision when it comes to naming the 23 players that must be submitted to UEFA for the championship.
"Kevin Foley, John O'Shea, Paul McShane, Darren O'Dea, Shay Given had all been carrying knocks and we have been monitoring them closely in their recovery."
Ireland open up their campaign against Croatia on June 10 before facing Spain and Italy.
Republic of Ireland Euro 2012 squad:
Goalkeepers: Shay Given (Aston Villa), David Forde (Millwall), Keiren Westwood (Sunderland)
Defenders: Stephen Kelly (Fulham), Paul McShane (Hull), Sean St Ledger (Leicester), Stephen Ward (Wolves), John O'Shea (Sunderland), Richard Dunne (Aston Villa), Darren O'Dea (Celtic),
Midfielders: Paul Green (Derby), Glenn Whelan (Stoke), Aiden McGeady (Spartal Moscow), Keith Andrews (West Brom), Kevin Doyle (Wolves), Damien Duff (Fulham), Darron Gibson (Everton), Stephen Hunt (Wolves), James McClean (Sunderland).
Forwards: Jonathan Walters (Stoke), Shane Long (West Brom), Simon Cox (West Brom), Robbie Keane (LA Galaxy).
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