Does he imagine Jose Bosingwa doing to the diminutive Argentine what Ashley Cole has so often done to Cristiano Ronaldo? Or are the images darker and more disturbing? Does he even dare consider what a destructive force Messi could prove in the absence of suspended left back Cole?
Messi finished as runner-up to Ronaldo at FIFA's world player of the year gala in January but against Chelsea here this evening he is expected to prove himself the finest footballer on the planet. A South American genius whom even Diego Maradona believes could become his superior. The greatest the world has ever seen.
World beater: Messi
At Barcelona, the confidence in his considerable ability is extraordinary. Yesterday Xavi was asked how someone who is just 21 deals with all that pressure and expectation. The Spaniard who also made it into FIFA's top five in Zurich did nothing to deflect the attention away from his young colleague.
On the contrary. 'Leo is the best player in the world,' declared Xavi without hesitation. 'And he is capable of making the difference in the semi-final and even the final. He does not feel the pressure. He just enjoys playing. I think he will be fantastic for us.'
Previous form: Xavi tussles with Ashely Cole - who will miss tonight's match - during the Champions League group stages in 2006
He is fantastic. Born in a small town north of Buenos Aires but bred in Barcelona, he has been waiting for this moment since he first arrived in Spain as a 13-year-old who needed a three-year course of growth hormone to make him taller. Newell's Old Boys, the club in Argentina that nicknamed him 'the flea', could not afford the medication. Barcelona could and lured him away.
Looking at him now, it would seem it was meant to be. The drugs propelled him to a relatively modest 5ft 7in a height that did not stop Maradona almost single-handedly winning the 1986 World Cup.
'The Flea': Messi in action for his beloved Argentina
The comparisons with the man who now manages the national team go way beyond that, however, for the one they even call Messidona. Thierry Henry watches him in awe, in training as well as matches. 'The only person I have seen do such things is Maradona,' said Barca's former Arsenal captain. Samuel Eto'o says he is 'the one who makes us dream'. Or, in Hiddink's case, have nightmares.
It is Messi's presence that appears to convince seasoned admirers this is the best Barcelona team in the club's distinguished history. Better than Johan Cruyff's 1992 team and better even than the side Ronaldinho inspired to 2006 Champions League glory (Messi missed the final due to injury suffered against Chelsea).
The next eight days will go some way to determining if they are that good. Eight days that will see them meet Chelsea either side of a potentially decisive La Liga clash with Real Madrid.
But if the pressure is on Messi to deliver, he appears to deal with it in the most understated way. He really does do his talking on the pitch. As those who attended the FIFA gala in Zurich would have noted, he is the antithesis of Ronaldo. Only one player dared appear on the stage in a gold lame jacket. Only one player would crash his Ferrari in a tunnel on the way to training.
Messi drives the sensible Audi which the club give all their senior players and when you click on to the 'dress like Leo' section of his official website, you'll find not a stitch of designer gear but £15 adidas training tops.
In his Barcelona kit he does look brilliant, though. A blur of red and blue with a ball seemingly cemented to his feet until he either creates an opportunity for Eto'o or Henry or scores himself. He has scored 33 goals this season not dissimilar to Ronaldo at Manchester United en route to winning the Champions League and the English championship.
Barcelona do have weaknesses that Hiddink will want to exploit. Theycan be defensively fragile. Hiddink probably imagines Didier Drogbabattering a defender not considered good enough to remain part of Sir Alex Ferguson's plans at Old Trafford.
GerardPique has started more Champions League games than any other member ofPep Guardiola's squad this season but he will be seen by Chelsea as theweak link.
The Spaniards nevertheless sound confident. Xavispoke of how they are better than the side that lost to United lastseason and top of a league superior to England's.
ButChelsea, as Hiddink insisted, have come here with the intention ofattacking and scoring an away goal. Of seeing Frank Lampard, MichaelBallack and Michael Essien somehow dominate a Barca midfield of Xavi,Andres Iniesta and Yaya Toure.
That particular battle could determine how much Messi sees of the ball he so loves. 'Whenyou prepare the game in your mind you never lose,' said Hiddink lastnight. 'But sometimes the reality can be more cruel.'
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