Football's world governing body FIFA believes that six of 12 Brazilian stadiums that are to host the 2014 World Cup may not be ready in time, the daily Folha de Sao Paulo reported on Tuesday.
The paper cited a study by a FIFA consultant on the stadium construction or renovation program pointing to various degrees "of risk" for arenas in Manaus, Cuiaba, Porto Alegre, Curitiba and Sao Paulo.
But the biggest concern is for the stadium in the northeastern city of Natal because of a "tight schedule" that left no "margin for problems", it added.
Manaus and Cuiaba have "medium risk" while Curitiba and Porto Alegre have "low risk", with a greater chance of being ready in time.
The report indicated that two years before the World Cup gets underway, work on the 12 stadiums have progressed on average by 34.4 percent.
"The outlook for the 2013 Confederations Cup is even more critical. FIFA reports delays in three of the four venues for the competition," Folha said.
In a statement, FIFA however said the document cited by Folha was an internal monitoring report developed at the end of April for stadium experts.
"This document is for the stadium experts and can be easily misinterpreted without the respective background information on the various evaluation criteria and parameters," it noted.
"What is important though is the significant progress which has been made at the venues for the FIFA Confederations Cup Brazil 2013, particularly Recife, Rio de Janeiro and Salvador," football's world governing body said.
The Confederations Cup, seen as a dress rehearsal for the World Cup, will be held from June 15 to 30 next year in four confirmed cities: Rio de Janeiro, Brasilia, Belo Horizonte and Fortaleza. Recife and Salvador could be added depending on progress on the work.
But the FIFA report said challenges facing the Recife arena "will be hard to overcome", complaining about the "bureaucracy and excessive politicization" in the country while acknowledging President Dilma Rousseff's determination to speed things up.
Earlier this month, FIFA and the Brazilian government agreed they would each have a representative on Brazil's Local Organizing Committee for the World Cup.
Brasilia will be represented on the committee by Luis Fernandes, a trusted Rousseff lieutenant, whose appointment was seen by analysts as necessary to avoid a collapse of the tournament and to speed up the preparatory work.
Brazil plans to spend billions of dollars to build or modernize stadiums, airports, road and public transport for the World Cup.
But costs for temporary installations such as space for fans, the media and guests were not factored in, which will drive up overall costs.
FIFA has for months complained about delays in renovation or construction of stadiums as well as infrastructure projects for the first World Cup in Brazil since 1950.