Peter Keeling on the mutual respect that has flourished between Europe's top two clubs

It is one of football's best-kept secrets. In 1956 Santiago Bernabeu, patriarchal president of Real Madrid, begged Matt Busby to take over as manager, telling him: "Leave Manchester for Madrid and I will give you a paradise." To which the master of Old Trafford replied: "My heaven is in Manchester."

He turned down the greatest job in world football at the club that won the first five European Cups, staying loyal to United, the team he had taken over in 1945 when the club office was a Nissen hut. Busby had to wait until 1968 for his beloved club to be crowned kings of Europe.

Through the rest of their lives Busby, Bernabeu and the then United chairman Louis Edwards built on their friendship as the special relationship between the clubs flourished.

After the 1958 Munich air disaster, when it was found United had been underinsured, Busby asked Real to play his team in a fund-raising game.

His son Sandy reveals: "Mr Bernabeu told my dad he had a nerve to ask him a favour after turning down his offer of a job. He then turned to his secretary and told her to find a date in his club's schedule as soon as possible to play United just for the expenses of the trip."

United's current chairman Martin Edwards said: "There has always been a tremendous mutual respect since that first year we met in Europe, in 1956-57. We lost to Real in the semi-finals after beating Borussia Dortmund and Athletic Bilbao. We also lost in the quarter-finals in 2000 to Real after a goalless draw in Madrid."

Edwards said of the first meeting: "Real had some fantastic names: Di Stefano, Gento, Kopa. The following year when they beat Milan in the final 3-2, the brilliant central defender Santamaria was added.

"By the time the final of all finals was played in Glasgow, with Eintracht Frankfurt beaten 7-3, the legendary Puskas was in the side, scoring four of the goals."

Standing in the Hampden Park crowd on May 18th, 1960 was Alex Ferguson, then 18 and starting to make his name in the Scottish game. He says: "That is one match I will never forget. It was spine-tingling."

United's manager may have more reasons to remember tonight's encounter after recent controversial remarks will ensure a hostile reception from the Bernabeu faithful. Although well known for his ball-hopping comments, Ferguson may have got this call badly wrong.

Peter Keeling is the author of Masters of Old Trafford (Robson Books)