Manchester United boss Sir Alex Ferguson has backed Cristiano Ronaldo to break the 20-goal barrier for a third successive season.

The Portuguese star, who racked up 42 last time round as United romped to a Premier League and Champions League double, has 13 to his name so far.

"People are saying Cristiano has not had a good season, but he has got 13 goals and 11 assists," said Ferguson.

"If you dismiss last season altogether, they would be saying it is incredible for a winger to score 13 at this stage. I am absolutely certain he will end up with over 20 again," added the United boss.

Ferguson added that it was impossible for Ronaldo, now one of the most heavily-marked players in the Premier League, to repeat his "miracle season" of 2007/2008 when he was also named world player of the year.

"It's hard to replicate a season like that but I am not sure that Cristiano understood it was a miracle season," said the United manager.

"He had the belief it was normal for him and I think he just expected to carry on. But one of the situations he had to face was that this year couldn't be as good as last season. Now he has started to come to terms with the whole thing, we will see more goals from him," he said.

Ronaldo suffered an ankle injury at the start of the season and was at the centre of a long-running controversy caused by Real Madrid's attentions.