Dunne is set to face Ronaldo and Manchester United at Old Trafford on Sunday.
Dunne said: “At times he can be running so fast any nick sends him tumbling. He makes the most of the situation, I suppose.
“Some referees give free-kicks but some don’t. He is the best player in the world and he plays the game to his advantage.
“Diving or not diving, he’s impossible to mark when he’s on form.”