The push for a more patient-centred NHS could be compromised by plans to restructure local health bodies, according to experts.
PCTs are in charge of commissioning services
NHS boss Sir Nigel Crisp has ordered England's 303 primary care trusts, which commission services, to make cuts of 15%, and in some cases merge.
But think-tank the King's Fund said the measures could derail reforms such as giving patients a choice of hospitals.
And health services managers added the changes must not compromise care.
PCTs are responsible for three-quarters of the NHS budget, using it to ensure enough hospital and GP services are provided in each region.
But Sir Nigel, the chief executive of the NHS, has told them they must be reconfigured to bring themselves in line with council social services boundaries.
There are about 150 social services departments across the country and, while not every PCT and social services boundary will have to match, there is expected to be a significant reduction in the number of trusts.
King's Fund chief executive Niall Dickson said while the proposals largely made sense, there was a danger some of the government's key reforms could be jeopardised as local health bosses grapple with the changes.
He said the pace and volume of the changes was concerning.
"We're already seeing the huge financial strain that new reforms, such as patient choice and payment by results (where hospitals are paid for the treatment they provide to patients) are placing on the service and the last thing we should be doing is diverting the attention of managers and health professionals from this demanding agenda."
From the end of this year, patients will be given a choice of up to five hospitals for treatment, including one private provider.
John McIvor, of the NHS Confederation, which represents PCT managers, said he was not opposed to the changes.
But added: "The quality of primary care services provided to patients must not be compromised by the government's call for savings."
Sir Nigel said the measures "complemented" current government policies.
And he added they would prepare the health service for the white paper due out later this year on improving out-of-hospital care.
PCTs have until the autumn to agree the changes with regional health bosses.