Ahead of Saturday's big game James Robson looks at the Barca stars who pose the biggest threat to Manchester United's quest for the Champions League.

Defence key player – Gerard Pique

How different might the 2009 final been if not for Pique’s intervention in the early stages?

United started in Rome like a team ready to win inside the first 15 minutes.

And when Cristiano Ronaldo burst through on goal, he looked set to score in his second Champions League final in succession, following his header against Chelsea in 2008.

But his former United teammate, Pique, had other ideas.

His cynical block stopped the Portuguese winger in his tracks on the edge of the area. A classic case of taking one for the team – and hardly the sort of rough-house treatment you would associate with Barcelona’s artists.

But there is another side to Pep Guardiola’s brilliant side – a steely edge that means they can mix menace with magic. In Pique – who spent four years at Old Trafford from the age of 17 – they have a player who perfectly encapsulates that mix of silk and steel.

He might not have flourished at United – struggling to get first team opportunities ahead of Rio Ferdinand and Nemanja Vidic – but his career has gone from strength to strength back at the club where he began his life in football.

Since leaving United in 2008, he has won three La Liga titles, the Champions League and World Cup with Spain. Add in a pop star girlfriend in Shakira, and life is sweet for the 24-year-old.

Defence might be seen as the weakest link in Barca’s armoury – but it hasn’t stopped them sweeping all before them in Spain and reaching two Champions League finals in three years.

Former Liverpool midfielder Javier Mascherano is expected to partner Pique in the centre of defence, which might be an area United look to exploit aerially, given the Argentine’s diminutive stature.

That would mean Carles Puyol covering at left back, with the thrilling Dani Alvez on the right.

Midfield key player – Andres Iniesta

Andres Iniesta stamped his name into the consciousness of every United fan with his outstanding performance in 2009.

Before that Rome final, Lionel Messi was seen as the man United had to stop. Afterwards it became clear that Iniesta is the main supplier of his bullets.

A player blessed with beautiful balance and the ability to thread the ball through the eye of the needle.

Always with the space and time to pick out the perfect pass, Iniesta allies that with the technique to dribble past players at will.

The scorer of Spain’s winning goal in last year’s World Cup, Iniesta is the man for the biggest occasion.

The Iniesta-Xavi-Messi axis is central to Barcelona’s success in recent years – but it is not all about the ‘tiki taka’ football that leaves opponents in a daze.

Guardiola’s insists on a work-rate of the highest tempo to put opposition teams under pressure from the first whistle until the last.

The taskmaster is said to demand his team retrieve possession within 10 seconds of losing it – and judging by the way his players hunt in packs, invariably they manage to do just that.

With Mascherano likely to play in defence, it will be Sergi Busquets who will fulfil the role of ball-winner and will be expected to tee up those blessed with more flair.

One such player is Xavi who, alongside Iniesta, has the ability to pass rivals into oblivion.

For so-long underrated, he is now considered pivotal for both club and country and regarded as one of the finest passers of the ball in the world.

Attack key player – Lionel Messi

Not simply a forward, he is an irrepressible force of nature that can play wherever he wants and still be devastating.

At times impossible to knock off the ball, his close control and dribbling leaves opponents with twisted blood.

Coming from Argentina, where every up-and-coming talent is earmarked as the ‘new Maradona’ no one has come closer to filling Diego’s boots.

The world player of the year and focal point of a side full of stars at the Nou Camp, Messi will be the man giving Sir Alex Ferguson nightmares in the build up to the final after hitting 49 goals for Barca this season.

His wonderful solo goal against Real Madrid in the first leg of the semi-final was typical of his ability to win a match single-handedly. His header in the 2009 final against United, evidence that even given his diminutive stature, there is nothing he cannot do.

But if Messi doesn’t get you, David Villa almost certainly will.

The man who puts Fernando Torres in the shade when playing for Spain is arguably the best striker in the world.

Ferguson tried to bring him to Old Trafford last summer, but his heart was always in his homeland – and a move to Barca, a match made in heaven.

But after a brilliant start and 22 goals in all competitions, Villa’s form has dipped of late.

He is still expected to start at Wembley, with Ferguson even utilising Michael Owen in his position in training in an attempt to work out a way to stop Barca’s deadly marksman.

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