In the freezing fog that yesterday hung over Milanello, the secluded training ground between the bustling city and the lakes, Milan began training as usual at 11.30am. Some light fitness work; a series of exercises to work on ball possession; a short match played on half a pitch. The good news was that influential midfielder Clarence Seedorf was training again after injury. The bad news was that defender Alessandro Nesta, back to his awesome best this season, was still working alone in the gym, trying to shake off a niggling thigh injury.
About 15 miles away, at Appiano Gentile, Internazionale were also going through their training routines. Faced with a squad heavily depleted by injury, Jose Mourinho was forced to draft in five players from the youth academy to make up the numbers. The sight of playmaker Wesley Sneijder – arguably Inter's most important player this season – leaving early, having missed the session with flu, was a further worry.
In many respects it looked like business as usual at both camps, but beneath the surface, and across the city, the tension is slowly ratcheting up ahead of tomorrow night's derby at San Siro, the most eagerly awaited for years, one that could go a long way to determining the outcome of the scudetto.
The ' derby della Madonnina' - named after the statue of the Virgin Mary on the city's Gothic cathedral – is a thoroughly Italian affair, but at the heart of the drama tomorrow will be two exports from English football, and two of the biggest personalities in the modern game: Mourinho and David Beckham.
Inter's Portuguese coach, having last season maintained Roberto Mancini's record of domestic success but continental failure, is now putting his own stamp on the nerazzurri. Hired to deliver the European Cup, which Inter last won in 1965, he is developing a squad which is more of a "team", rather than a collection of gifted stars, and is less predictable.
But Mourinho's influence is limited once the match begins, which is when Beckham can take centre stage. The England international has again been rejuvenated by the Italian experience, and in return he appears to have revived Leonardo's team. Playing a new attacking role, Beckham's mix of technical expertise and hard graft has been a major factor in the rossoneri's post-Christmas form.
Arrigo Sacchi, who steered Milan to two European Cup triumphs before guiding Italy to the 1994 World Cup final, believes Beckham is likely to be the victor. "Milan are arriving at this important match in excellent shape, physically and mentally," he said. "Beckham's been a great signing for Milan and one of the reasons that they're turning things round. And there is a limit to how much a coach can influence the outcome of a single match."
Sacchi is the man who recommended Beckham to Milan in 2008 having known the player in his time as sporting director of Real Madrid. He added: "It didn't surprise me that he bedded in so quickly at Milan because he's an intelligent person. Very few English players who have played in Italy have made an impact. Intelligence in football is not an optional extra and he's intelligent, so he's been able to adapt more easily than others. Tactically, he knows how to move in relation to his team-mates. He's always active – with or without the ball. This is a notable quality." Plus, there was his attitude. "At Madrid he struck me immediately as an immense talent, a great professional, a real hard worker, and a serious and reliable person. A model player, one who loves his football."
Leonardo said Beckham was just as motivated as last year, when he was also on loan from LA Galaxy. The Brazilian, then one of Carlo Ancelotti's assistants, added: "He is so open to whatever I propose tactically that there has been speculation that he might even play as a full-back, but that's not something we have tried in training yet."
The only time Beckham has looked uncomfortable since returning to Milan was when he was ambushed outside a restaurant this week by a TV presenter for a satirical programme. She grabbed his crotch – theoretically to test whether his advertisements for Armani underwear, which are on billboards all over Milan, are accurate. That incident aside, he has looked at home.
Riccardo Silva, owner of the club's TV channel, said: "Everybody was taken by surprise by Beckham. They expected the Hollywood superstar, but he was polite and respectful. He's the exact opposite of his image. What's most surprising is that he is quite shy. I saw him last week at a party without Victoria. There were people there who had had a few drinks who were physically trying to force him into the presence of some fashion models to see what would happen and he wasn't having it.
"He's very aware about his behaviour in public and how it might be perceived. He's a very smart guy. If he wasn't, everything that goes on around him would have destroyed him by now."
By contrast Mourinho's abrasive nature has won him plenty of critics, especially among the sports press, as La Repubblica's Michele Serra explained. "Italian journalists don't like him because he treats them badly," he said. "He breaks with convention, says what he thinks, and is not interested in some kind of fake fair play."
But Mourinho's stock among football men – players and coaches – could not be higher. Saachi said: "As a person he's cultured, intelligent, clear-sighted and a perfectionist. As a coach, you just have to look at his record. He's won everywhere. He knows how to win, he knows how to produce teams with great character and consistency. He has an excellent relationship with his players despite being severe with them at times. He can manage human resources and communicate like few others."
Sacchi believes that with Inter having brought in so many new players this season – including Samuel Eto'o, Thiago Motta, Sneijder and Diego Milito – Mourinho's team is still developing. "He inherited a team that was used to winning in a certain way, with players getting results on the basis of their individual ability or physical strength. [The dependence on Zlatan Ibrahimovic would be a good example.] This year Mourinho brought in players who could help him synthesize the play, communicate the collective idea to the others, to create a better team unit. But he's been unlucky so far with injuries to key players."
Mancini tipped Inter to go on and win the title but said that Milan had "the chance of a lifetime" to avenge a 4-0 humbling by Inter in August which raised questions about the decision to replace Ancelotti with the rookie Leonardo. "Milan are in form and Inter are looking a bit worse for wear," noted Mancini.
They are nevertheless a team which simply refuses to die. Just as at Chelsea, Mourinho has forged an unbreakable spirit among his players. Last week they came back from two goals down at Bari; the previous week they trailed Siena 3-2 after 88 minutes, but won 4-3. That is the main reason why Milan's midfield enforcer, Gennaro Gattuso has singled out Mourinho as the man his team fear most.
There is a wider aspect to this local squabble. Next month Manchester United and Chelsea visit San Siro for the first legs of Champions League ties against, respectively, Milan and Inter. Sir Alex Ferguson and Ancelotti will both be observing their opponents tomorrow, with the former doubtless taking a keen interest in Beckham's role.
The interest is mutual for neither Italian team hide the fact their priority is Europe. Mourinho has been specifically hired to win the Champions League. Massimo Ambrosini, Milan's captain, this week confirmed his team's focus when he said he would "sign up straight away" when offered a theoretical deal in which Inter win Serie A, and Milan the Champions League.
Given both Milan teams are something of a work in progress, with Mourinho refining Mancini's approach, and Leonardo establishing his own philosophy, tomorrow should provide Ferguson and Ancelotti with a guide as to their chances.