The city that bested Chicago to host the Games this week announced structural problems will force the closing of a brand-new soccer stadium and the United Nations is being called in to finish construction on another venue.
The 60,000 seat Joao Havelange stadium in Rio is just six years old but newly discovered roof problems could put crowds in danger.
"I asked if this represented a risk for spectators and they told me it did, depending on the wind speed and temperature," Rio Mayor Eduardo Paes told reporters. "On that basis, I immediately decided to close the stadium until we had more details."
The stadium, roughly the size of Chicago's Soldier Field, was built just before the Pan-American Games in 2007 and featured prominently in Rio's pitch to host the World Cup in 2014 and the Olympics in 2016.
Earlier this month, the Brazilian government agreed to pay the United Nations $17.6 million to help finish a new soccer stadium in Brasilia.
The IOC says it is "absolutely confident" in Rio's preparations for the 2016 Olympics despite the temporary closure of the stadium that will host track and field events at the games.
International Olympic Committee spokesman Mark Adams says the IOC is "in regular contact with Rio 2016."
Adams tells The Associated Press "there are still more than 3½ years to go before the games and we are absolutely confident that they will deliver."
Track and field's governing body said it is monitoring the situation.
The Associated Press contributed to this report.