It was at the skating rink in Barcelona that Deco announced his intention to move. This was a photo - shoot arranged by his kit sponsor, and the venue prompted thoughts that either Deco was there to demonstrate that even with blades on his feet he could outpass most footballers, or else his relationship with his then employers was on such thin ice his career was in danger of sinking irretrievably. He smiled at the jokes, kept his cool, said he wouldn’t stay where he wasn’t wanted and that he was fairly sure where he would go.

By that day last May, the queue had already formed across the top of Serie A and within the Premier League. As soon as Luiz Felipe Scolari decided he would be joining Chelsea as manager, he assured Deco he wanted him. Theirs has usually been a profitable alliance and no player has been more important to Scolari’s adventures in European football. Deco is the Brazilian his compatriot Scolari ushered into the Portugal squad in spite of some grumbling about passports of convenience; Deco is the footballer Scolari immediately assigned a role as ringmaster for the implicit demand that Chelsea become a more pleasing side to watch.

Different managers have asked different things of Deco, and most, moving on, tend to want him in their new teams. Once it became known that Barcelona were ready to let him leave, the Inter-nazionale of Jose Mourinho, who had worked with Deco at Porto, showed an interest, just as Mourinho’s Chelsea had four years earlier, when his price stood a great deal higher. Barcelona argue that £8m for a player into his 30s represents good business but his absence has already been noted. “Still in search of the new Deco,” moaned one headline in Catalonia last week. He had been the barometer of the Barça team that won two leagues and a Champions League, their coach Frank Rijkaard used to say.

So a sense of elegy hung over that day at the ice rink when Deco effectively said goodbye, and an element of mystery, too. What had become of Barça’s barometer? By the beginning of this year, Deco had been identified by some of Barcelona’s strategists as a footballer in decline and a man too strongly associated with the gradual drift from champions to complacents.

In April, the player took personally a suggestion by one director that certain players had faked injuries. Deco had also found it necessary to argue that, as adults, footballers were entitled to go out in the evening, a candid response to whispered questions about how some of Barça’s players, like the Brazilians Ronaldinho and Deco, managed their social timetables.

Suffice to say Chelsea’s new midfielder has not been recruited from a monastery. Nor have coaches as demanding as Scolari, Mourinho or Rijkaard ever hesitated before assigning him a heavy workload. In Mourinho’s Porto teams, winners of consecutive league titles and the Uefa and European Cups, Deco was known as o Magico, conspicuously the man without the straitjacket in a side of rigorous positional organisation. “We had a really well- defined midfield triangle,” as Mourinho described it, “and Deco was the one who was allowed to shift his position with some freedom. It meant we could keep possession sometimes to an exaggerated degree, and he was always on the lookout to create danger from that.”

It might be suggested, too, that in that overachieving Porto team Mourinho put an exaggerated emphasis on his outstanding player. With some of the vanity that characterised Mourinho as a young manager, he once showed off the notes he made during a tense European semi-final when he was banned from the touchline. Deco’s name dominates those notes.

Deco had worked hard to become the leader of a Champions League-winning team, mind. In his early twenties he was one of dozens of talented Brazilian players who crossed the Atlantic to play in Portugal. He had been at Corinthians in Brazil, where his then colleague, Sylvinho, recalls a small, quick-foot-ed teenager with particular tenacity. “He’s an example of why it’s wrong to categorise Brazilian players as just about great technique and skill on the ball,” says Sylvinho. “He’s got the defensive parts to his game as well.”

Benfica recognised some of that, although in the period Deco was trying to make an impression in Lisbon, he found their manager, Graeme Souness, unpersuaded. He drifted out on loan, and then with longer-term contracts, to lesser Portuguese clubs. Porto readjusted his horizons and before very long both Brazil and Benfica were wondering how they had let this one slip through their fingers.

His decision to play for Portugal followed several years of being ignored by Brazil managers - including Scolari - and, he tends to say, was based on a genuine emotional attachment “to a country that has shown me so much affection”. Besides, he adds, “Eusebio played for Portugal”. And as every Portuguese-speaking schoolboy knows, Eusebio grew up elsewhere, in Mozambique.

Would Deco get into the Brazil team now? Presumably. Would he fit into a side that also included an inform Ronaldinho and Kaka? On the evidence of the past four years, yes, emphatically. Moving from Porto to Barcelona in 2004 not only put Deco on a more elevated stage but advertised the range of his football and what Scolari consistently refers to as his “intelligence”.

As Barcelona, with Ronaldinho their emblem, emerged as Europe’s outstanding club team between 2004 and 2006, Deco redefined his game, playing deeper, part of a three-man midfield usually made up of creative types - himself, Xavi, Andres Iniesta – and apparently short of muscle. He was no longer the No 10 but charged with a variety of tasks. “The fact is that if I hadn’t adapted my game when I came here, then I wouldn't have had a place in the side,” he explained. “Barcelona had Ronaldinho, who was the natural No 10 in the side. In Portugal I had been playing in that sort of position, but I always had the ability to do the more defensive work, too. And if you look at the game generally now, coaches are giving up the idea of the No 10. They say to those sorts of players, you’ve got to be a forward or you’ve got to be a central midfield player, otherwise you’re not in the side. Even if you’re a Zidane and you come into the game now, you’re going to be put up front or on the wing.”

So, at Chelsea, you won’t hear Deco participating in too many debates about whether his midfield game is compatible with those of Frank Lampard or Michael Ballack - two players, incidentally, he spoke highly of long before they became colleagues - because he would regard it as his responsibility to make sure it is. He will not score the same type of goal from midfield as they do, but he will provide regularly for them and contest confidently with them the right to take free kicks from outside the penalty box. He has scored from one such already, one of two goals from his first two Premier League games. Ahead of the most testing fixture so far, Alex Ferguson calls Deco a “nice footballer”, and “the big change in their team from last season”. The nice footballer will not make Chelsea any less feisty in midfield, but will help them to entertain.