Organizers in charge of the city's preparations said the man died while dismantling a crane used to install the roof of the Arena da Amazonia.
It wAs the third death of a worker in accidents in or near the stadium in Manaus in less than a year.
The local government identified the 55-year-old Portuguese man as Antonio Jose Pita Martins, who worked for the Portuguese company Martifer, a multinational focused in metal constructions.
Brazilian media said he sustained head and chest injuries when he was hit by a metal bar in the early morning accident. Organizers said the cause of the accident was being investigated.
An inspection visit by the Amazonas state governor at the stadium Friday was cancelled because of the death. Gov. Omar Aziz had been expected to announce the date of the venue's inauguration.
FIFA and the local World Cup organizing committee said in a statement they "deeply regret the death of the worker."
Brazilian President Dilma Rousseff also released a statement lamenting the death.
Brazil has been under a spotlight because of its problematic World Cup preparations, with the southern host city of Curitiba still in danger of being dropped because of a delay in stadium construction. The country also is making headlines because of fan violence and turmoil in the Brazilian league, which may not start on time because of a series of civil lawsuits against a sports tribunal decision that altered last year's final standings.
The Arena da Amazonia is one of the five stadiums still under construction less than five months before the World Cup, although local organizers said construction at the site was almost 97 per cent completed when the accident happened. It will host four World Cup matches in June, including England vs. Italy and the United States vs. Portugal.
Organizers said Friday's accident did not interfere in the construction of the stadium. The crane had been removed from the venue's main construction area and was at a site across the street.
In December, a worker at the Arena da Amazonia died after falling 115 feet while working on the stadium roof, prompting a work stoppage of four days as authorities inspected safety conditions. Another worker died there in March after falling from a scaffold and hitting his head. Also in December, a worker died of a heart attack while paving an area outside the venue.
In late November, two workers were killed when a crane collapsed while hoisting a 500-ton piece of roofing at the stadium that will host the World Cup opener in Sao Paulo. In 2012, a worker died at the construction site of the stadium in the nation's capital, Brasilia.
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