"Bobby is an indvidual who never blows his own trumpet and puts himself down in relation to some of today's players," Giles told RTE. "I don't think it's right.
"If Bobby genuinely feels that way, and I'm sure he does, it's fair enough but I don't think anybody could describe Ronaldo as being better than Best.
"Anyone watching that match tonight, apart from the shot he had that made the goal, saw it was not an aberration. You never saw Best do some of the things Ronaldo did tonight and in other matches.
"I saw Best have poor games and he was a genius but I never saw him indulge himself in the way Ronaldo does.
"I'm surprised by Charlton's comments. You have to bear in mind Bobby is Manchester United and a huge, iconic figure around the world of football. He's employed as a director by Manchester United and gave great service as a player.
"I have the deepest respect for Bobby, everyone who knows him knows he's a wonderful man but he gets asked questions and dragged into it and making these invidious comparisons.
"There's really no question Best would never have done things you've seen Ronaldo doing tonight. Entertainment is beating three players and pulling the ball back for someone to stick it into the net. That's what football entertainment is.
"Ronaldo does it occasionally but, on a lot of other occasions, he's indulging himself. It's not entertainment and it certainly doesn't entertain me."
He continued his blast against Ronaldo: "He's very self-indulgent. There's 60,000 there in that stadium and if any of them went to see Ronaldo, they should see him try behaving like a professional so they can go home and say I've seen something tonight.
"What they've seen is an impersonator, a clown. A self-indulgent idiot really doing crazy things. He's not really playing for his team and not doing his talents justice.
"The thing about great professionals, if you're number one in the world, you have to behave in a certain way.
"I've seen it too often from Ronaldo. Clowning around, cheating, diving. All that stuff. This isn't the Harlem Globetrotters, this is football.
"He's an absolute disgrace to the game. He is a petulant brat poncing around all night.
"I hate to see him acclaimed by the world of football."