Plans to transform the NHS in England could lead to cuts in hospital beds and community services, leading nurses have warned.
The Royal College of Nursing (RCN) said proper funding for the process was key to making sure the strategies "solve instead of exacerbate" problems in the health and care system.
The comments come as new analysis conducted by the British Medical Association (BMA) concluded that there is "nowhere near enough" funding to deliver on the plans.
Health managers in 44 areas of England have been ordered to draw up sustainability and transformation plans (STPs) setting out how they will reduce costs, change services and improve care in their region.
But following Freedom of Information requests to each of the areas, the BMA said that in order to deliver the plans, the NHS in England needs at least £9.5 billion of capital funding.
Responses from 37 of the 44 footprint areas found that more than half of the STP footprint areas have told NHS England they would need more than £100 million of upfront funding to make changes.
A handful have quoted capital needs of more than £500 million.
Meanwhile, figures released in October revealed that the NHS is facing rapidly rising maintenance fees - with NHS facilities needing more than £2 billion to pay for outstanding "significant" or "high risk" repairs.
Dr Mark Porter, chairman of the BMA's council, said: "The NHS is at breaking point and the STP process could have offered a chance to deal with some of the problems that the NHS is facing, like unnecessary competition, expensive fragmentation and buildings and equipment often unfit for purpose, but there is clearly nowhere near the funding required to carry out these plans.
"These plans are fast becoming completely unworkable and have instead revealed a health service that is unsustainable without urgent further investment, and with little capacity to 'transform' in any meaningful way other than by reducing the provision of services on a drastic scale."
Commenting on the anaylsis, Tom Sandford, director of England at the RCN, said: "While the aspirations of STPs may be admirable, the lack of any financial commitment from the Government is their Achilles' heel.
"We have always supported the aims of the plans - preventing ill health, joining up services, delivering care closer to home.
"But proper funding - and consultation - is key to making sure STPs solve instead of exacerbate the problems of England's health and care system.
"We remain concerned these plans will be used to make savings, and short-term cuts to hospital beds and community services will be made without any plans for the long-term change envisaged by NHS England.
"We hope this will be the final warning the Government needs to act on what is now a health and care funding crisis, and the March budget reflects this new reality."
Labour's shadow health minister Justin Madders added: "This significant intervention from the BMA shows again that the Government is failing to support the plans of local health communities by giving them the money they need to make the STP process work.
"It is one thing asking local health and social care leaders to get together and shape the services they need for the future, but by refusing to match the plans with appropriate funding the Government is undermining the work that is being carried out and setting them up for failure.
"It is time for the Government to take the blinkers off, listen to the experts, and recognise the scale of investment that is needed to make the NHS fit for the future."
An NHS England spokeswoman said: "Rather than just commenting from the sidelines, local health and care leaders and clinicians are coming together to actually try and solve some deep-seated problems by identifying practical ways to improve services.
"Yes, there are well-known pressures and constraints facing the NHS, but for patients' sake we should obviously all try and make the best of the situation, rather than just stand to one side and say, 'well, I wouldn't start from here'."