Alex Ferguson is convinced that Cristiano Ronaldo could reflect on a brilliant season even if he 'only' scored 20 goals.

The World Footballer of the Year reached double figures with his penalty against Derby at Old Trafford earlier this week.

It was his first goal in domestic combat since mid-November, an extraordinarily long barren run by Ronaldo's standards.

Indeed, Ferguson's assistant Mike Phelan claimed the Portugal superstar was purposely introduced against the Rams with the intention of ending his drought.

Ferguson insists Ronaldo has not been suffering a crisis of confidence. However, he does feel the 23-year-old's phenomenal 42-goal haul last term might be used as an unfair benchmark throughout his career.

"You do have these exceptional seasons," said the Scot.

"But it is very hard to replicate them every year. I remember Ruud van Nistelrooy got 44 one year - the next it was 30, and he is a centre-forward.

"Ronaldo is a very confident lad and has belief in his own ability.

"Yes, he has been missing a few chances that he was putting away last season but he has made 10 goals for us this year and scored another 10.

"At the end of the season I am sure he will be over 20 and that is a fantastic return for a winger."