Sir Alex Ferguson has hailed Cristiano Ronaldo's work ethic and value to the club amid reports that Manchester United have agreed to sell him to Real Madrid at the end of the season.

Ferguson, speaking in Japan before the fresh rumours of a possible move emerged in the Spanish press, was full of praise for the Portuguese star who has been at Old Trafford for five years.

"Over the five years he has been with us, we have seen him develop into the player he is today," he said on the sidelines of the Club World Cup.

"He always had certain attributes that pointed him towards the very top -- his amazing skill, his speed and his courage. In the time he has been with us, he has developed his decision-making," added Sir Alex.

He has also become a master marksman, which Ferguson said was down to "practice, practice, practice."

"As a kid he played centre-forward for Sporting Lisbon and our people in Portugal kept telling us that 'this boy is a great goalscorer.' When he first came to us, we couldn't see that. All of a sudden he just blossomed and last season he got 42. That is a measure of a young person wanting to do well, to improve himself by his own determination and ambition to practise all the time," he said.

His comments came as the respected Spanish newspaper El Mundo reported that United and Real Madrid have a gentleman's agreement to transfer Ronaldo to the Bernabeu at the end of the season.

It said the two teams agreed in principle to the deal at the end of a tug-of-war for the Portugal star this year but pledged a vow of silence.

El Mundo quotes a conversation this week between a Real Madrid director, Pedro Trapote, and one of his business associates, and says at least two other senior club sources have leaked the news.

Ronaldo was touted all summer as an 80 million euro ($115 million, 74 million pounds) Real target, with United furious at the Spaniards' constant efforts to prise him away from Manchester.

The 23-year-old is currently earning 120,000 pounds a week in a deal through to 2012 but could buy himself out of the contract at the end of the season.

To counter this, reports in England said last month that Ferguson had instructed the Old Trafford hierarchy to work on a new deal to ward off further Spanish overtures.