Alex Ferguson says Cristiano Ronaldo is a better player now than when he left Manchester United for Real Madrid, and that the step-over king is the man United need to stop in his tracks tonight.

Fergie has also described United’s Champions League visit to the Bernabeu as the “acid test” for his team of Premier League champions elect.

The Red Devils appear on an unstoppable march towards their 20th domestic top flight title, but Fergie knows they are yet to come up against a foe as formidable as Jose Mourinho’s charges this season.

"Ronaldo is the one to worry about," Fergie said, ahead of his showdown with the superstar he nurtured.

"His speed, his goals, he plays every week, never asks for a rest. These qualities are exceptional. He was a young man when he left us, but he has flourished and is a better player now."

"The acid test is [against Real], no doubt about that, and we have to get through to win this competition, no doubt," Fergie added.

“But there's a great spirit about this team and they deserve recognition. It's unfortunate we're meeting this early. I wish it had been at Wembley [in the Champions League final]."

Fergie may realise that his team is facing a great challenge tonight, but the belligerent Scot is uncowed.

Asked if he thinks United can triumph against Real and go all the way to Champions League glory, he laughed and said:  "Our team? I think so, yes."