Attending an Olympic forum in Sydney, Coates told delegates that construction had not commenced on some venues, infrastructure was significantly delayed and water quality was also a major concern two years out from the Games.
He warned, however, that there was no “plan B” to find another host.
“I think this is a worse situation than Athens,” said the Australian, referring to preparations for the 2004 Games, which were plagued by construction delays.
“In Athens, we were dealing with one government and some city responsibilities. Here, there’s three.
“There is little co-ordination between the federal, the state government and the city – which is responsible for a lot of the construction.
“And this is against a city that’s got social issues that also have to be addressed; a country that’s also trying to deal with the FIFA World Cup coming up in a few months.
“It’s the worst that I’ve experienced.”
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.
Rio’s Mayor Eduardo Paes said the city “has to accept the criticism and work hard.
“We have to work with great zeal and dedication in order to deliver everything on time,” the news site G1 reported him as saying.
Local Games organisers pointed out they were moving in the right direction.
“The time has now passed when general discussions about the progress of preparations contribute to the journey towards the Games,” Rio 2016 said in a statement.
“It is time for us to focus on the work to be done and on engaging with society.”
They noted that important decisions were taken recently on the Games budget and said improved communications between federal, state and city authorities were reaping benefits. They also urged the IOC to get behind the city.
“The support of the International Olympic Committee is also crucial,” the statement added.
“We have an historic mission: to organise the first Olympic and Paralympic Games in Brazil and in South America. We are going to achieve this. In 2016, Rio will host an excellent Games that will be delivered absolutely within the agreed timelines and budgets.”
The IOC announced a series of measures earlier this month to kick-start lagging preparations.
“These measures include dedicated joint task forces with the organisers, recruitment of a local construction manager, creating a high-level decision-making body bringing together the IOC, government and all key partners of the project, and more regular visits by Olympic Games executive director Gilbert Felli,” the IOC said in a statement.
“Mr Felli has received a very positive response on the ground in the past few days, and a number of recent developments show that things are moving in the right direction.
“Now is a time to look forward to work together and to deliver great Games for Rio, Brazil and for the world, and not to engage in discussion of the past.
“We continue to believe that Rio is capable of providing outstanding Games.”
Under the spotlight
Brazil has been under the spotlight for the more immediate concern of the soccer World Cup finals starting in June.
Amid problems with stadium construction, labour unrest and security in other parts of the country, thousands of troops were deployed to Rio’s slums in February to wrest them back from the control of drug gangs and criminals.
Coates has made six visits to Rio as a member of the IOC’s coordination commission.
Although Rio organisers boasted the same number of staff as London’s two years before the 2012 Games, they lacked experience, Coates said.
He pointed to only two staff working in the Games’ tests department, though test events were scheduled to start this year.
As Australian Olympic Committee president, Coates also spoke of the country’s sports leaders and team managers “not getting answers” to any of their questions on visits.
“Can they use the carparks in the village for recovery centres? What will be the time to take from this venue to this venue?
“All of those things, they’re being fobbed off.
“But again, we just have to make it happen – and that’s the IOC’s approach. You can’t walk away from this.
“If it comes off – the first Games on the South American continent, in a magical city in so many ways – it’ll be a wonderful experience for the athletes.”
(Reporting by Ian Ransom, additional reporting by Andrew Downie, Editing by Amlan Chakraborty/Patrick Johnston/Pritha Sarkar/Toby Davis)