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Every team has a star, a leader or a key player that is pivotal to its success or failure. If a side doesn't have one, it means they're not good enough to win anything - much less even be at the World Cup. All the favorites for this year's World Cup have a key player - but with domestic seasons coming to an end, an update on the form, fitness and quality of these players is required before you put your bucks on the team that they lead.

Brazil: 5/2 favorites - Key Player: Ronaldinho

Ronaldinho, the best player in the world, is having his best season of his career. His club, Barcelona, is running away with La Liga and they are the favorites to win the Champions League.

If there is any worry, it is that Ronaldinho may burn out after playing so much soccer this season - a concern that has been expressed by the Brazil team coach, Carlos Alberto Parreira. But this is wishful thinking on the part of the Brazil's rivals who know that Ronaldinho and Brazil at the peak of their powers will be virtually untouchable. However, although Ronaldinho may be ready to set the World Cup alight, problems plague the rest of the side. The Brazilians are either suffering from a lack of form (Kaka, Dida), can't get into their club side's starting 11 (Robinho, Julio Baptista), are hated by their club team-mates and are suffering 'personal problems' (Adriano), need to lose weight fast (Ronaldo), are getting on a bit in age (Cafu, Roberto Carlos) or are prone to horrific defensive errors (Roque Junior, Lucio). Ronaldinho might have to win the World Cup despite, rather than because, of his Brazilian teammates.

Argentina: 7/1 - Key Player: Juan Roman Requelme

Argentina has gone under the radar of most World Cup commentators. However, slowly but surely they're gathering attention and, more crucially, momentum. Even their playmaker, Joan Roman Requelme, is a relative unknown. Discarded after a poor spell at Barcelona, Requelme is now plying his trade at Villarreal, a small and unglamorous Spanish club. Somehow, Villarreal - a town without a taxi rank and only two hotels - is in the Champions League semi-finals. Requelme has made this possible, and is starting to show his immense talent on the international stage. He goes into the World Cup in the finest form of his life, and is one of the few players in the World Cup that can elevate his side beyond the reach of its rivals. Incidentally, Argentina has one other player that can do this - Lionel Messi, the 18-year-old at Barcelona. The combination of the two may power Argentina to the final.

Germany: 7/1 - Key Player: Michael Ballack

There are certain reasons that Germany - a struggling team - has obscenely short-odds. Firstly, they're hosts, and home teams have an unnerving tendency of winning the trophy in their own back yard. Secondly, their World Cup history of seven World Cup finals and three wins (including being runners-up in 2002) means you can never write them off. Finally, they have Michael Ballack. The goal scoring midfielder from Bayern Munich is the one genuine top-class player in a mediocre German outfit, and he has had a solid if unspectacular season at his club. But he is currently in talks to move to Chelsea, which must be unsettling for him. Also, he's not the kind of all-encompassing, overwhelming player that can lead an inferior side to victory like Maradona did with Argentina in 1986. If Germany can get further than the quarter-finals, it will be a testament to their never-say-die attitude rather than their soccer abilities, and probably because Ballack has had yet another storming tournament.

England: 13/2 - Key Player: Wayne Rooney

England may have a number of stars; Beckham, Gerrard, Lampard and company - but only one precocious 20-year old has the talent to lead the English to glory this summer. Wayne Rooney has been in scintillating form for Manchester United this season. United's poor early season - with early exits from the English FA Cup and the Champions League - has meant that Rooney has been playing considerably less games than most top-class players on the plane to Germany, and so he remains relatively fresh for the World Cup. He was the shining light in England's stop-start qualifying campaign, and strikes genuine fear into opponents. Whether he strikes gold as well this summer, remains to be seen - but he's playing well enough to see England lift the trophy.

The Netherlands 11/1 - Key Player: Ruud Van Nistelrooy

The ever-talented Dutch looked impressive in the qualifying stages - especially as they cantered to victory in a group that contained Czech Republic and Romania. They are spearheaded by Manchester United striker Ruud Van Nistelrooy and are reliant on him to score the goals required to push them into the later stages. But problems have emerged. Despite Van Nistelrooy vying for the English Premiership's golden boot this season, he has lost his place in Manchester United's starting line-up to French striker Louis Saha. Though slowly making his way back into the United side - this has unsettled the usually unflappable Van Nistelrooy. It's possible that he will be unprepared, and so may under-perform in Germany. In the toughest of World Cup groups (with Argentina, Serbia & Montenegro and Ivory Coast), the Dutch can't afford to shoot blanks.

Italy 8/1 - Key Player: Francesco Totti

Italy is in magnificent form, recently thrashing World Cup hosts Germany, 4-1. Their star player, Francesco Totti had led his club side, Roma, to 11 consecutive victories in Serie A - an Italian record. And then he got injured. It was almost inevitable that at least one star player will come a cropper before the finals begin in June, and Totti is struggling to recover in time. The Azzuri will remain strong contenders, and have a deep squad (in fact it's arguable that Fiorentina's Luca Toni is far more important to Italy's chances), but a player of Totti's class will be missed.

France 10/1 - Key Player: Thierry Henry

There aren't enough superlatives to describe Thierry Henry. He is a stunningly, fantastically, amazingly brilliant player for Arsenal. Currently, he is taking his young club side to new heights in the Champions League by playing some of the most exquisite soccer the competition has seen. Yet, his club form never seems to translate into international dominance. At the last World Cup and European Championships, his performances were poor and the belief was that he was a big match choker. But maybe, if his Champions League performances are anything to go by, he's over this stage fright now. If so, France - which in this pundit's opinion is horribly underrated - is a good bet to go all the way.

Spain 13/1 - Key Player: Raul

Raul has consistently been one of the best players in Europe for a number of seasons. Now 28 years old, he should now be in his prime and ready to take a talented Spain side onto elusive World Cup glory. But his current poor form for his club, Real Madrid, suggests that Spain will underachieve once more. Raul suffered a cruciate ligament injury in November, and the belief is that he hasn't recovered. Without Raul at his best, Spain will remain good, but not good enough.