The Great North Run is facing a "struggle" because of issues getting insurance in case it has to be called off due to Covid-19, the founder says.
Sir Brendan Foster said "the key tool" in holding major events was missing and there had been "a huge market failure".
He said organisers faced being liable for costs and called on the government and insurance sector to meet.
The government said it was aware of the "wider concerns" around securing indemnity and was "exploring" support.
The Association of British Insurers (ABI), which represents the sector, said it was "happy to continue to engage with the government".
The Great North Run - the world's largest half marathon - was set to celebrate its 40th anniversary in 2020 but it had to be held virtually because of coronavirus.
This year's event is due to take place on 12 September, with about 57,000 adults set to run between Newcastle and South Shields.
Sir Brendan said organisers were "cautiously optimistic" it would take place but they would look to hold an alternative if the event was unable to go ahead as planned.
"We will struggle, we will have to look forward to see how we can do it, we will have to see what shape we can do it," he said.
He said an indemnity scheme needed to be guaranteed across the live event sector by 21 June, when legal limits on social contact are due to be removed as part of the prime minister's roadmap out of the pandemic.
"It's not the last hurdle, it's the first hurdle, because if you don't get over this hurdle, the commitment to organise the event will be struggling," Sir Brendan said.
"This is not about the Great North Run, this is about the government seeking to bring it back to normal and seeking to make sure that Britain gets back on its feet by the autumn.
"Unfortunately, to open up these large events and to ease the restriction on these large events, the key tool in doing that is missing at the moment because the insurance industry is not available to offer insurance."
The government said its events research programme would consider how effective various measures were at reducing transmission risk at large events, including using testing.
"The programme will start this weekend with pilot events carried out across a range of settings, venue and activity types," it said.
The ABI said it had made it clear to the government "the very limited risks" the commercial market was able to provide cover for.
"With the Covid-19 public health emergency continuing to present a significant risk of cancellation or disruption, commercial insurers remain unable to offer this type of cover, or only at a cost that is unaffordable for many," a spokesperson said.
"Insurers continue to provide support for a wide range of other risks, and event organisers should discuss their needs with their insurance advisers, who can fully explore all insurance options in the market."