He told the Sunday Mirror: "I'm often asked whether Cristiano can still improve as a player.
"My answer is that he can, if he keeps developing as a person off the pitch.
"Cristiano is an exceptional player. But most times it is the 'me-me-me show'.
"He is always looking for satisfaction in individual moments. He wants the team to shine on him. But it should be the other way. He should be shining on the team.
"In 2008 Cristiano had a period that he was only busy to please himself.
"In the weeks leading up to the Champions League final against Chelsea in Moscow I decided to go and confront him and work on him.
"I told him that he could make the difference in the final for United if he was prepared to make himself less important than the team.
"And he did!
"Cristiano is an intelligent boy who can accept criticism. But that selfish part of his character is difficult to cut out."