In another incident in Manaus, the death of a second worker, Jose Antonio da Silva Nascimento, was reported by Brazilian state television after his body was found in a convention centre close to the stadium.
Earlier on Saturday, 22-year-old Marcleudo de Melo Ferreira became the third stadium worker to die since last month when two men were killed after a crane collapsed onto the roof of the Corinthians Arena in Sao Paulo.
In all, five workers have died on stadiums being built for next year's soccer showpiece while a sixth was killed working on the Palmeiras arena in Sao Paulo, which will not be used to host World Cup matches but could serve as an official training base.
De Melo Ferreira died in hospital in the early hours of Saturday after a cable snapped and sent him falling 35 metres (115 feet) from the roof of the 605 million Brazilian reais ($262 million) Arena Amazonia, where work has been stepped up to 20 hours a day to ensure it does not slip any further behind schedule.
It is due to be ready by Jan. 15.
Statements issued by FIFA and Andrade Gutierrez, the construction company which employed De Melo Ferreira, expressed regret and an investigation into his death has begun.
Miguel Capobiango, the co-ordinator for UGP Copa, the umbrella co-ordination organisation for all World Cup projects in Manaus, told Reuters on a site visit last Wednesday that construction time on the stadium had been increased and workers were now operating in three shifts for all but four hours a day.
"The stadium will be ready in time and we will not let FIFA or anyone else down," he said, speaking against a background of industrial noise in the stadium where hundreds of men were working on the roof, on the ground and within the stadium itself.
But this week in Curitiba, around a quarter of the 1,200-strong workforce went on strike, further delaying construction on the 265 million reais Arena da Baixada, which had been expected to be the last of the six remaining projects to be completed before the Sao Paulo crane collapse.
Although the stadium is the cheapest of all 12, its construction has been among the most problematic with complications surrounding its three stakeholders -- Atletico Paranaense, the Parana state and the city of Curitiba delaying its transformation into a modern 42,000 seater ground that will, like Manaus, stage four World Cup matches.
More than 250 men went on strike on Tuesday demanding back pay from November and another 50 joined them in a demonstration on Friday, bringing the streets around the stadium to a standstill.
Although strikes are not uncommon on building projects in Brazil, this one is deeply embarrassing for those involved in the World Cup project.
The Arena da Baixada was described as "a mess" by senior FIFA sources at the draw for the World Cup finals at Costa do Sauipe last week and is not due to be ready until the second half of February at the earliest when a test match will be held.
Its projected inauguration is March 26 - less than 12 weeks before it is due to stage its first World Cup match between Iran and Nigeria on June 16.
Mauro Holzmann, the executive marketing director of Atletico Paranaense, who will play at the stadium after the World Cup, told reporters at a news conference at the stadium on Saturday that the strike would be settled by Monday.
"It was a small problem, a misunderstanding and it won't happen again," he said.
"We had trouble getting access to government funds to pay the workers. Put it down to Brazilian bureaucracy."
However, workers interviewed in Curitiba on Saturday said they had still not been paid and the strike would continue on Monday if the situation continued.
To add to the woes of the authorities, the builders workers union said it was considering calling for a separate strike on Monday to protest about working conditions.
In a separate news conference later on Saturday, Curitiba Mayor Gustavo Pruet told reporters the strike regarding the backpay would not delay the project further and there was no question the stadium would fail to meet its March 26 deadline.
"Yes the men went on strike this week, but the issue has now been solved," said Pruet.
"The stadium will be ready. We have problems to overcome and we will overcome them, there is no doubt about that. This city will be ready for the World Cup.
"The world champions Spain are preparing here and using the city as their base and we are very proud of what we will bring to the finals."