Routine operations could "cease for several months" if hospitals have to deal with a major flu outbreak this winter, an expert has warned.
Planned - or elective - operations such as knee or hip replacements could be put on the back burner if the NHS struggles to deal with the additional demands of a bad flu season, the Society for Acute Medicine (SAM) said.
The comments come as a separate poll found that more than nine in 10 health and care leaders across England are "concerned" about their organisation's ability to cope this winter.
Dr Nick Scriven, president of SAM, which represents hospital doctors who look after patients admitted as an emergency who do not need surgery, said a bad flu season could "overwhelm" the NHS.
NHS England boss Simon Stevens last month warned hospitals to be prepared for a "pressurised" flu season following a heavy outbreak in the Southern Hemisphere during winter there.
Mr Stevens said the health service was reviewing the situation in Australia and New Zealand, where hospitals were forced to close their doors to new patients and people faced long waiting times.
But Dr Scriven said that despite talk of preparations, doctors on the frontline feel as though there is "nothing new other than crossed fingers".
"Over the last two to three years we haven't had to deal with any major outbreaks of infection such as norovirus or flu, but this year we are predicting a bad flu season that will overwhelm us after what we've witnessed in Australia and New Zealand," he said.
"For all the talk of preparations, on the ground it feels as though nothing's new this year other than crossed fingers - which is fair comment as the government has failed to tackle effectively the issues behind the pressures we face."
"If, as we expect, we see a flu outbreak, I think the NHS - in terms of both beds and clinical staff - will break far worse than last year and elective activity will almost certainly cease for several months."
Meanwhile NHS Confederation surveyed 131 health leaders - including chief executives and non-executive directors of organisations including NHS acute hospital trusts, community services and mental health trusts - to find out how concerned they were for their organisation's ability to cope during the forthcoming winter.
It found that 57% admitted they were "extremely concerned" while an additional 35% were "concerned". Just 8% said they were confident their organisation would cope well throughout the season.
"The health and care system in England is in a fragile state and it is fair to say many organisations will struggle to meet expectations over the next few months," said Niall Dickson, chief executive of NHS Confederation - a membership body for NHS providers and commissioners.
"Last year it was said that the service was 'just about coping', but for many of our members this year looks more challenging.
"Not only is there the prospect of ongoing pressure - high bed occupancy and delayed transfers of care blockages - but the worry too of a serious flu attack combined with bad weather."