Hospitals may have to close under reforms to the NHS in England, a report from the NHS Confederation suggests.
The findings, reported in the Observer, criticise ministers for not explaining the need for the reforms, describing some of the process as "extraordinarily risky."
The confederation represents bodies such as foundation hospitals, primary care trusts and doctors' groups.
The Department of Health said the reforms would improve the NHS.
Under the changes, contained in a bill to be published this week, GPs will be given more responsibility for spending much of the budget, hospitals are to be set free from central control and an independent board will oversee services.
While the NHS Confederation accepts that reform of health service structures in England is necessary, it appears to be unhappy with the way ministers are going about it, the Observer reports.
The confederation said the government was indulging in "unpleasant" and "demotivating" attacks on managers whom it was purging, while still asking them to drive the reforms through.
It also said that allowing GPs to commission services from what is called "any willing provider", could mean the closure of some hospitals and facilities in order to make way for new private providers.
The Department of Health said that modernisation was "a necessity, not an option", and the Health and Social Care Bill would "increase autonomy and accountability at every level in the NHS."
Shadow health secretary John Healey described the report as a "comprehensive demolition job," amounting to a big red light ahead of the legislation.
A Department of Health spokesperson said while the NHS budget had been protected by the government, "it must still simplify its structure and cut bureaucracy, which will release further savings to invest in care for patients".
According to The Observer, the NHS Confederation report will also raise concerns over the new system under which consortia of GPs will be able to send patients to whichever provider they judge will offer the best treatment, warning that this will force the NHS to shrink in order to make space for new healthcare providers.
The policy of "price competition", allowing hospitals to undercut one another to attract patients, poses a risk to standards of care, the report is expected to warn.