Financial pressures could get in the way of the drive to improve care following the Stafford Hospital scandal, experts say.
Figures released last week showed nearly one in three NHS trusts is forecasting a deficit this year.
Now a review by the Nuffield Trust - published a year on from the Stafford public inquiry - said money worries could hamper efforts.
The warning was echoed by inquiry chair Robert Francis QC.
He criticised what he saw as the "oppressive reactions" of the system to hospitals that ran into trouble with budgets and hitting targets.
He said hospital leaders needed to be "frank" about whether they could provide high-quality care with current levels of funding.
"It is unacceptable to pretend that all can be provided to an acceptable standard when that is not true," he added.
'Safety and quality'
Mr Francis was responding to a report by the Nuffield Trust based on in-depth interviews with 50 staff at five hospitals and online feedback from chairs and chief executives of 53.
Many reported they were taking action to improve care, but their overwhelming concern was that the state of finances was going to harm their ability to succeed.
One hospital chairman said: "The one good thing Francis has done, the really good thing, is that it has ensured that safety and quality have become more prominent - that's really important.
"But I am left with a real concern about the doability of it all and the need for us to find a way forward."
But despite these concerns, Mr Francis said he was pleased with the reaction to his report, published exactly a year ago, as many of his recommendations had been accepted.
"The strong message sent out to the health service by government was that important and fundamental change was required," Mr Francis said.
But he added that this represented "only a start" and that the emphasis on quality of care needed to continue.
Julie Bailey, founder of Cure the NHS, the campaign group that led the calls for the public inquiry, said she was disappointed the government had not agreed to full regulation of healthcare assistants, as the Francis Inquiry had recommended.
But she added that overall she was pleased with the progress being made.
"Things are moving in the right direction. I believe people working in the NHS have a real appetite for change."
The publication of the report came after Health Secretary Jeremy Hunt praised the "Francis effect" in a speech to NHS staff in London on Wednesday.
"Twelve months on, we cannot expect to have solved everything or have completely transformed the culture of the country's largest and finest institution.
"But we have seen a real shift in priorities - new inspections, more nurses and a stronger voice for patients with compassionate care starting to replace tick-box targets as the major focus on boards and wards."