The LA Galaxy striker is aware of the level of ability possessed by the Portugal captain and believes that the game will provide a stern test for the Boys in Green
The Boys in Green conclude their summer friendly schedule against Paulo Bento's World Cup-bound team in New Jersey and the Real Madrid forward is expected to be deemed fit to play in the game.
Speaking ahead of the clash, Keane paid tribute to Ronaldo, identifying him as one of the best players in the world and said that it would be a "good test" for the Ireland players to play against the 29-year-old.
"Himself and [Lionel] Messi are clearly the best two players in the world and every player wants to play against the best players in the world," the LA Galaxy striker told reporters.
"It's a good test for the players to be playing against him. We certainly hope that he does play because you want to play against the best."
Ireland boss Martin O'Neill agreed with Keane's assessment of the Portugal captain and praised the "magnificent" talent of the former Manchester United attacker.
"He has this image that he likes to portray: get the shirt off, that type of stuff, but he's a magnificent player," said O'Neill. "He's absolutely superb. As Robbie said, just when Messi looked as if he was streets ahead of people, Ronaldo stepped up to the mark."
Meanwhile, O'Neill has indicated that he would like to see more of Ryan Meara after the New York Red Bulls goalkeeper took part in a training session with the Irish squad on Monday.
Born in the United States, Meara had previously been called up the the Ireland Under-21 squad by Noel King but the shot-stopper was unable to take part due to club commitments.
"We thought it was an opportunity and he came and trained with us. He's going to come to our game tomorrow night with his grandfather so we'll keep an eye on things," said O'Neill.
He added: "I'd obviously need to see more of a him. It would be hard to make a judgment on a 15-minute game in one training session."
O'Neill is expected to make a series of changes to the squad that drew 1-1 with Costa Rica in Philadelphia, with Glenn Whelan and Marc Wilson out of contention, while injury concerns hang over Shane Long and Shane Duffy.
Ireland face Portugal on Wednesday June 11. Kick off 00:45 BST.