GP practices are set to be handed responsibility for most health services under ministerial plans for a radical shake-up of the NHS in England.
Local trusts and strategic health authorities would be sharply scaled back to make way for their new role.
Health Secretary Andrew Lansley believes GPs are best placed to understand patients' needs and to decide where money should be spent.
But there are concerns GPs may not have the skills or will to take on the role.
Others have questioned how they would be held accountable.
Discussions with doctors' representatives over the plans are continuing, and the government has confirmed it will publish further details in a white paper next week.
The NHS budget currently stands at £100bn a year. About 80% of this is given to local health managers working for 152 primary care trusts, which in turn commission services for their areas.
The plans involve setting up groups of practices which would work together in consortia, then buy in management skills, possibly from people doing the same job for existing primary care trusts.
The consortia would take charge of billions of pounds of funds for mental health, hospital and community services.
The NHS budget has been protected by the coalition government, and is not subject to the severe cuts of other Whitehall departments.
But the health service has been told to save up to £20bn by 2014 to help it cope with the ageing population, rising drug prices and lifestyle changes such as obesity.
The Royal College of Nursing has claimed almost 10,000 posts - double the number from two months ago - are being cut despite government promises to protect frontline services.
The white paper is also expected to make reference to the creation of an independent NHS board to oversee NHS services.
The acting chief executive of the NHS Confederation, Nigel Edwards, told BBC Radio 4's Today programme there were "some quite significant risks" in transition to the new system.
"Obviously it is going to take time to implement this and the PCTs at the moment are the people who keep the lid on the performance and financial management of the system," he said.
Mr Edwards also said the reform would move the NHS from a market where large organisations place big contracts, to one similar to the gas or telecoms market, where demand is shaped by many individual purchasing decisions.
"I think the concept here is lots of individual decisions by GPs - when they make referrals and send people to hospital - will be added up and we will have a greater market dynamic," he said.
"GPs will also help plan services and direct strategy for hospitals by telling hospitals what they need for the longer term."
Mr Edwards said he expected many GPs to recruit former staff from PCTs to help them cope with the additional workload, which will involve "quite a big step up from what they've been doing before".
The move to having GP consortia controlling spending has long been championed by Mr Lansley - and in recent months the British Medical Association has indicated it is open to working with the government on the idea.
Dr Laurence Buckman, chairman of the BMA's GPs committee, said: "We will have to see the details, but there is certainly a willingness to look at this."
He added the plans had the potential to improve services as GPs were "much quicker to respond to patients".
And Professor Steve Field, chairman of the Royal College of GPs, said: "From what we can glean, the direction of travel is the right one."
Dr Mike Dixon, chairman of the NHS Alliance, a group of doctors who support GPs getting involved in commissioning, agreed.
"Staff on the front-line know what is good care and what is bad care. They are more sensitive to the needs of patients and I think this will lead to better outcomes."
A spokesman for the Department of Health said details of its plans for a patient-centred NHS would be published in a white paper shortly.
He added: "In recent speeches, the Health Secretary has set out the values and vision for an NHS centred on patients.
"He has already emphasised the need to liberate the NHS to focus on outcomes and improving results for patients.
"And in a speech to the BMA on 2 July, he highlighted the importance of empowering doctors and nurses in the NHS to deliver quality standards and services. The details of how this vision will take effect will be set out soon."
Shadow health secretary Andy Burnham said: "More than anything else, the NHS needs stability right now. Instead, we have an £80bn political experiment.
"It exposes deeply flawed thinking."