Published Wednesday, 14 November 2012
McClean in action for the Republic. (© Getty)
It comes despite the Derry-born winger's outburst on social media when he was left out of the squad for September's World Cup qualifier against Kazakhstan.
Trapattoni said the game at the Aviva Stadium on Wednesday night presents big opportunity for McClean to make an impact.
"There are only one or two players in the world who can make the difference along," the Italian boss told reporters.
"I said he has a great opportunity to achieve in this important moment, to transform - show us your attitude and your commitment."
Meanwhile the FAI has confirmed goalie Keiren Westwood has been ruled out of the game after undergoing a scan on his groin.
The 28-year-old will be replaced Millwall keeper David Forde, who will win just his fourth senior cap.
A spokesman for the Football Association of Ireland said: "The Football Association of Ireland today confirmed that Keiren Westwood has been ruled out of tonight's game against Greece in Aviva Stadium with a groin injury.
"Keiren underwent a scan this morning, and will return to his club later this evening for treatment. David Forde will replace him for tonight's game."
Kickoff for the friendly will be at 7.45pm.