When he first arrived at Old Trafford back in 2008, the Brazilian's style of play earned him a reputation as defender who was liable to make the wrong decision in key areas.
However, this season he has established himself as United's senior right-back, picking a number of plaudits along the way.
The latest has come from Irwin, who believes that the 22-year-old has learned from his mistakes.
"There has never been a question about Rafael's talent. He was brave, aggressive and his attacking qualities were very good. He had all the attributes. His problem was that as a young player he was impetuous and the timing of his tackles got him into trouble and caused problems," Irwin told the Manchester Evening News.
"It is all well and good being aggressive but it was learning how to do it properly at the right times. He has had to learn to be a lot more patient with his defending. He had been trying to win things too early. He wanted to win the ball when it wasn't feasible.
"You have to learn to hold back. You learn with age and experience that you cannot win the ball all the time. There is no doubt that in that area he has come on a lot. His defending has improved and it will get even better. It is horrible to say but you learn the most when you make mistakes and he has made a couple of big ones on big occasions.
"He'll never forget them. When you make those kind of mistakes it clicks with you and you become wiser."
Rafael has made 27 appearances in all competitions this season, scoring two goals.