ATP chairman Andrea Gaudenzi has warned that if professional tennis does not resume by August then there will be major "problems" to salvage a season severely disrupted by the coronavirus pandemic.
Tennis has been in lockdown since the start of March when Indian Wells was called off days before the start of the prestigious tournament.
Tennis authorities have said there will be no action until at least July 13, while Wimbledon have announced the cancellation of the 2020 tournament, for the first time since the Second World War.
The French Open, originally slated for the end of May and start of June, has been moved to September, and Gaudenzi believes more events can be saved, but only if the season can get back underway in August.
"If we manage to start again in August, we'll save three [Grand] Slams and six Masters 1000, otherwise the problems will increase tenfold," Gaudenzi said in an interview with several Italian media outlets.
"We are working on the hypothesis of four weeks on clay after the US Open, with Madrid and Rome before Roland Garros."
Gaudenzi said no sanctions would be taken against Roland Garros for taking the decision alone to postpone.
"Now we are working together," Gaudenzi, 43, who took over as ATP chief in January, told Gazzetta Dello Sport. "Tennis needs unity, Paris acted out of fear, making a mistake. But they have recognised this."
All this will depend on the virus which has infected over 1.5 million people around the world, with the United States and Europe hit hard. According to the latest figures, more than 89,000 people have died while more than 337,000 people have recovered.
"We have made 50 versions of the calendar that we change day by day," said Gaudenzi. "I am confident that the season in America can begin with the August Masters 1000 in Toronto and Cincinnati and then the US Open.
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"In this way, three Slams and six Masters 1000 would be played and the season would be 70 per cent safe. Of course, if the whole American slot were to skip, the difficulties would increase tenfold."
Gaudenzi said the options were being examined in conjunction with the ATP Player Council including Roger Federer, Rafael Nadal and Novak Djokovic. He stressed it was hoped to maintain the ATP Finals, scheduled for London in November 15-22.
"The 02 Arena is only available in the week already fixed. I don't like closed doors, it's the last resort," he said.
To offset the blow to lower-ranked players and tournaments the ATP are also studying financial measures to help.
"Our system is solid, it can last a year without tennis, but not more than," the ATP chief said. "Talking about August, September, November is all hypothetical, we can't bang our heads against the wall for something that maybe won't even happen, because we could even start next year."