London - Manchester United manager Sir Alex Ferguson has warned his star striker Cristiano Ronaldo about his attitude, according to media reports on Sunday. The Portuguese winger, who has been strongly linked with a move to Real Madrid in the summer, has cut an increasingly frustrated figure this season and has been guilty of a number of acts of petulance.

His form has also suffered, and although he scored twice in the 3- 2 win over Aston Villa last week, it was his mistake that gifted Porto their opener in the 2-2 draw in the first leg of the Champions League last Tuesday.

That, clearly, is a concern for Ferguson.

"I don't accept that he will give goals away because of the player he is, I speak to him about it," he said. "I don't accept that from anyone."

"He always feels he's not getting the proper protection from referees and I think that, maybe, in quite a few cases he is right, and a few cases he is not right," Ferguson said. "It's hard when a player who wants to entertain doesn't get everything his own way. But you can't get everything your own way."

Ferguson said the Portuguese winger "understands that and there's not a problem with that. It's just a frustration that he feels he doesn't get the decision and he gets upset about it. I think, obviously, he doesn't enjoy that and he knows he's letting himself down more than anything."

United face the second leg of their tie against Porto on Wednesday. (dpa)