The Sunderland winger was named in Giovanni Trapattoni's 23-strong panel for the tournament in Poland and Ukraine and took to the social networking site to celebrate his inclusion on Monday.
“Absolutely honoured and couldn't be happier to have been called up to represent my country at the euros no better feelin! #COYBIG #ireland #euro12,” he tweeted.
However, some Twitter users made threats on McClean's life shortly after. The 23-year-old was born in Derry and took the decision to declare for the Republic of Ireland after representing Northern Ireland as a youth.
He declined an invitation to join the senior Northern Ireland squad in July 2011 in the hope of being recognised south of the border and that decision provoked hostility among a minority of Northern Irish football observers.
“F*** up your dirty fenian b****** il make sure you get shot when you set foot back into gods country #FTP,” one user tweeted.
Another said: “U deserve to be shot for that comment!! Your playing for Ireland and not the country you were born in (NI). #p****”
Both accounts have since been deleted.
McClean responded to the threats against him later in the day, saying, “Love the dogs abuse am gettin of shock N.I fans, just worry about watchin ur own country at the euros... oh wait #mybad #awkward haha.”
A PSNI spokesperson told the BBC: "We don't discuss individual cases, however, if we receive information that a person's life may be at risk we will inform them accordingly. We never ignore anything which may put an individual at risk."
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