"When it comes to sport, Northern Ireland has always punched above its weight," said the 27-year-old world number three in a video shown to the players on Saturday entitled 'Dare to Dream'.
"Remember these special moments," he added, over clips of Northern Irish sporting success that included the late Manchester United winger George Best in full flow in the country's green shirt.
Best never played in a European Championship or World Cup and Sunday's match in Nice will be the nation's first at a major tournament since the 1986 World Cup in Mexico.
"These sporting heroes helped unite Northern Ireland and now it's your turn," said McIlroy, a four-times major champion who met up with the players last month.
Northern Ireland, whose squad contains just five players from the English Premier League, also have world champions Germany and Ukraine for company in Group C.
"Coming home as a major champion was one of the proudest moments of my career so far," said Northern Irishman McIlroy.
"It's an honour for us to have the opportunity to represent Northern Ireland around the world ... and to put our wee country on the sporting map.
"Tomorrow you'll write the next chapter in our long and famous sporting story.
"When you walk out at that stadium in Nice, take a moment to think about our sporting icons, what they achieved and how this is your chance to take your place alongside them," added McIlroy.
(Reporting by Alan Baldwin, editing by Tony Jimenez)
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