A stadium in Brazil that was due to host athletics at the 2016 Olympics has been closed indefinitely because of structural problems with its roof.The Joao Havelange stadium in Rio de Janeiro was built only six years ago.It was also being used as the main football venue in Rio, while the city's Maracana stadium is being renovated for next year's World Cup.It is an embarrassment for Brazil as it prepares for its two huge sporting events, say correspondents.The authorities have also acknowledged delays in work on the Maracana and a funding problem at another stadium, which is set to host the opening match at the World Cup.'Not acceptable'Rio Mayor Eduardo Paes told a news conference on Tuesday that he had been told about the structural problems at the stadium - locally referred to as the Engenhao - earlier the same day."I asked if this represented a risk for spectators and they told me it did, depending on the wind speed and temperature."On that basis, I immediately decided to close the stadium until we had more details."He said the situation was "simply not acceptable" for a stadium which opened such a short time ago, and warned that those responsible would be held to account.The stadium opened late and over budget in 2007.It has since been leased to local football club Botafogo.