"I don't feel pressure playing in the Argentina shirt," he told reporters on arrival from Spain.
"In Spain I'm also in a team that has to win everything," added Messi, who helped Barcelona win their second consecutive title in La Liga at the weekend.
The world's top player flew into Buenos Aires to join coach Diego Maradona's Argentina squad who will begin their preparations for the World Cup finals on Thursday.
He was criticised by fans and some media last year for indifferent performances for Argentina as they struggled to qualify for the finals.
Having left his country as a young teenager to join Barcelona, they questioned his feelings of allegiance and commitment to the Argentine colours.
Messi, surrounded by a mass of tape recorders and microphones thrust close to his face, said he would do his best to transfer his trophy-winning form for Barcelona to the Argentina team.
"I will give my answers on the pitch and the World Cup is a nice opportunity to show Argentines I can do the same things in the national team as for Barcelona," he said.
Asked if Maradona should build the team around him, Messi looked bothered by the question and said: "Diego did not build the team for me, it's a team and we have to play for everyone (in it).
"I think (Argentina) are candidates (to win the World Cup). We are no-one's favorites because of the way that we got there. It could be good for us not to be favorites and we will have to prove ourselves on the field."
It will be Messi's second World Cup after Germany in 2006 when he saw little action and watched as an unused substitute when the hosts eliminated Argentina on penalties in the quarter-final in Berlin.
Argentina face Nigeria, South Korea and Greece in group B at the finals starting on June 11.
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