Ronaldo is Ferguson's grandest catch and the greatest threat

Cristiano Ronaldo says he will not celebrate a goal against Manchester United. Diplomacy is not called for here. A score for Real Madrid at the expense of his old employers in the Champions League would only confirm his majesty to both sets of supporters. A happy face would not equate to ingratitude.

Madrid's 80 million pounds wizard has been the greatest outside catch of Sir Alex Ferguson's 26-year reign. From the moment he left for Spain, Ferguson dreamt of bringing him back. Roy Keane was United's midfield locomotion for a decade and Eric Cantona was the ultimate nonconformist. The manager adored him, even with all the uproar. Peter Schmeichel's value in goal is almost impossible to over-state.

Ronaldo, though, was the purest expression of what United are about: unstoppable, sky-lighting talent that sends people home glowing. Even more than the marvellous Ryan Giggs, he was the link to George Best. Nearer to home Ferguson found Paul Scholes as well as Giggs: two of the greatest British footballers. But to capture Ronaldo he needed to wade into the Portuguese market and bring a 17-year-old wunderkind from under the noses of Barcelona and Madrid.

In scouting and recruitment this remains Ferguson's grandest kidnap.

Derided by some as a stepover-addicted show pony who would squeal under heavy tackling, Ronaldo found himself in a reverse finishing school. He was not over here to refine his skills. Under leaden skies he was in England to learn about physical adversity and find out what it takes to turn potential into immortality.

His team-mates helped, telling him not to yelp when tackled and encouraging him to ride out challenges and bully the bully with his brilliance. This is why the gratitude flows on both sides. For Ferguson, Ronaldo was the magic road out of the stagnation of the mid-2000s. With Wayne Rooney and Carlos Tevez, he led the way to the club's third European Cup win, against Chelsea in Moscow. In David Beckham's old No7 shirt,

Ronaldo was proving a point to himself. If he could prosper against Liverpool, Arsenal or Chelsea in tight, frantic, physical contests, he would have the resilience to assert himself in the more technical game played in Spain.

With that move to the Bernabeu, Ronaldo has sometimes radiated the borderline arrogance of someone who considers many of his team-mates to be too far beneath him ability-wise to bother involving them. Hence the early tendency to shoot from anywhere rather than pass to someone who might only muck it up.

Ronaldo's burden at Madrid is greater than Lionel Messi's at Barcelona, which is not to say Messi is the lesser player. In Catalonia the whole team are set up to facilitate Messi's genius and just about every player is creatively inclined. In Jose Mourinho's Real Madrid, organisation and strength are the foundations (not surprisingly, because who could hope to out-dazzle Barca?).

This has raised the glare of the spotlight trained on Ronaldo but also has doomed him to be seen as the second greatest player in a golden age. Of those bought since he left the Cheshire mansion belt, only Robin van Persie can approach Ronaldo's ingenuity level. United are more workmanlike than in 2007-09, when the pounds 80??million comic strip hero was at his English peak.

He won three Premier League titles and the Champions League before answering an urge to play in the white of Real Madrid.

Ferguson recalls the 2003 tie when Brazil's Ronaldo scored a hat-trick at Old Trafford and was clapped from the pitch by United fans. "That time they had the Zidanes, the Figos and Ronaldo - that galaxy of great footballers, but today they are far more professional," United's manager said. "I think they are far more organised and of course they have [Cristiano] Ronaldo.

"I think we have to recognise that their best player is the one we know all about. That's an advantage to us. I know exactly everything he can do in a game and how he tends to do things. Getting a player to understand that is a different thing but the boy Rafael has had a fantastic season for us, he's quick, he's aggressive.

"My faith would be in him to hopefully do the job. We don't worry about that. There's no point in going into the game worrying about Ronaldo and forgetting you have your own game to play."

Nor should Ronaldo worry about upsetting United's followers with a goal celebration. He has the right to enjoy his work, whoever the position.

Sensible United fans would expect him to stay true to his talent and know he is incapable of disrespect for Ferguson or their club. And if he scored a hat-trick, they would probably applaud him from the field.

Champions League draw for last 16

Galatasaray v Schalke 04

Celtic v Juventus

Arsenal v Bayern Munich

S Donetsk v B Dortmund

AC Milan v Barcelona

Real Madrid v Manchester Utd

Valencia v Paris St Germain

Porto v Malaga