Ricardo Teixeira, president of both the Brazilian Football Confederation (CBF) and the 2014 local organising committee, initially said on Monday that he was certain that the tournament would kick off in Latin America's largest city.
"We have absolute certainty and we desire that the World Cup opening will be in Sao Paulo," Teixeira told reporters after a meeting with Sao Paulo state governor Alberto Goldman and mayor Gilberto Kassab.
However, Teixeira later said in a statement that plans to use a new stadium built by the Corinthians club for the match had to be approved by football's governing body FIFA.
Corinthians also said that it was early days.
"There is a project for a 65,000 capacity stadium being analysed by the local and national authorities," the club said in a statement.
"This can only be definitively detailed and its costs and financing necessities calculated, after it has been revised and approved by FIFA."
Corinthians added that it was predicted that work would start next March and would be finished at the end of 2013 - too late for the Confederations Cup which will used as a dressed rehearsal.
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Confusion has surrounded Sao Paulo's participation in the World Cup since June when the local organising committee dropped plans to use the Morumbi stadium.
FINANCIAL GUARANTEES
The decision came after the city failed to provide financial guarantees for the cost of renovating the stadium.
Since then, hopes have been placed on the planned new Corinthians stadium in the sprawling eastern suburbs of the city. The club, one of the biggest in Brazil, announced it September that it would build a 48,000 capacity-stadium at a cost of 335 million reais (197 million dollars).
The stadium will be built and financed by the Odebrecht construction company which will be given naming rights in return.
However, FIFA demands a capacity of at least 65,000 for a stadium to stage the opening match at the World Cup, which would increase the cost and has become the subject of negotiations between the club and organising committee.
Goldman was confident the increased cost could be met.
"We believe that together, we can find a way out for this," he said. "We have managed to do everything we need to get to this point."
Monday's announcement came after a weekend in which armed attacks on world champion Jenson Button and a group of team engineers marred the Brazilian Formula One Grand Prix in the city, highlighting worries about crime rates.
Brazil was elected unopposed in 2007 to host the tournament which was earmarked for South America by FIFA under a short-lived rotation system which also brought this year's World Cup to Africa.
The country faces a huge job to improve its creaking stadiums and transport system, as well as fighting crime.
