Australia's Olympic chief John Coates, who in April branded preparations for the 2016 Rio Olympics as the worst ever, said on Tuesday the prognosis was now "much, much better".
Speaking at an event to mark two years until the start of the Rio Games, the International Olympic Committee (IOC) vice-president said Brazil's successful hosting of the soccer World Cup in June and July had been reassuring.
"I wasn't there but all of the reports to the IOC were good," Coates, who is a member of the IOC's coordination commission for the Rio Games, told a news conference in Sydney. "We had concerns about the airport and getting around but that all worked, the transport worked.
"It's a different event ... but over the last two months they've really put their foot to the pedal. We're back there officially at the end of September for another report but the prognosis is much, much better."
The first Games on the South American continent have been plagued by delays, rising costs and bad communication between different levels of the Brazilian government and organisers, prompting criticism from international sports federations.
Coates said he had received reports from the ongoing sailing test event in Rio that the water quality issue he had raised was being addressed.