Trapattoni has made it clear that Glasgow-born McCarthy, who withdrew from Ireland's Carling Nations Cup squad this week, is free to play for Scotland.
The Wigan midfielder, 20, has only played in a friendly for the Republic, meaning he could switch allegiance ahead of the Euro 2012 qualifying games next month because he has not played in a competitive match.
Trapattoni said: 'He is 20 years old, he can decide freely, 'I like Scotland, I like Ireland.' He has the possibility. He knows our position he knows we like him. He can decide. It's his heart that decides.'
There is speculation that Scotland boss Craig Levein may ask McCarthy to represent the country of his birth but Trapattoni seems indifferent to the possible implications of Scottish advances for one of the hottest properties in English club football.
The Ireland coach says he will include the midfielder in his squad for next month's Euro qualifier against Macedonia but insists there is no need for him to see him play Manchester United, Liverpool and Manchester City in the Barclays Premier Leaguebefore that game, adding: 'I don't need to go watch him. Marco Tardelli saw him four times.'
Kevin Kilbane will feature in next month's squad and captain Robbie Keane, who has suggested he may retire at the end of the Euro campaign, should also return.
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