Messi mystified by poor Argentina form
Messi has had an outstanding year with the Catalan club, helping to win the Spanish championship, the Champions League, Copa del Rey and Club World championship.
But he has struggled for Diego Maradona's Argentina, who crawled into the World Cup with a 1-0 win away to Uruguay in the last of their 18-match campaign and face Nigeria, South Korea and Greece in their first round group in South Africa.
"I don't know," Messi told reporters before FIFA's World Player of the Year award ceremony.
"I try to do the same as I do for Barcelona. But in the World Cup the qualifiers are complicated, sometimes it's difficult to play and it was a big effort for us to qualify.
"I believe the World Cup could be completely different for us, I believe it could be better for me and Argentina."
Messi is favourite win the award where he is joined on the shortlist by his Barcelona team mates Andres Iniesta and Xavi and by Real Madrid pair Kaka and Cristiano Ronaldo.
He is frequently upset by suggestions that he saves his best for his club.
"It bothers me a lot," he said. "I'm Argentine and I have a feeling for the shirt. I give everything for the Argentina team."
Like Messi, Portugal winger Ronaldo has not been able to enjoy the same sort of success with his country as he has at club level.
Portugal needed a playoff win over Bosnia to qualify for South Africa where they will face North Korea, Brazil and Ivory Coast in a tough first-round group.
The former Manchester United player said he believed they could spring an upset and drew inspiration from Greece's 2004 European championship win, when they beat Ronaldo's Portugal in the final.
"I have never won anything important for the national team but it's important for me," he said.
"Portugal have a chance, nobody spoke about Greece in 2004 and they won the tournament. I'm looking forward to a great World Cup, I'm really focused and happy to be there."