There could be a "glut" of hospital services shut down, a health expert has warned.
The NHS is under huge financial strain at the same time as grappling with workforce challenges - which could lead to some local hospital services being shut, said Chris Hopson, chief executive of NHS Providers, which represents frontline NHS leaders.
Mr Hopson called on Jeremy Hunt and NHS England boss Simon Stevens to admit that there is a disparity between what the NHS is being asked to achieve and the money that is available to do it.
"As we go round and talk to those smaller district general hospitals (DGH) that are running marginal rotas in lots of 'ologies' - rheumatology, dermatology etc - we are increasingly finding that people cannot find the senior consultant staff in order to keep those rotas up and running," he said.
"Our members tell us that they are struggling to keep services open because of workforce shortages and they therefore face really difficult decisions about; do you close down something either permanently or temporarily because you cannot staff it safely?"
He added: "NHS Improvement, when asking our guys to improve their financial position, one of the places they have been asked to look at is 'please identify your marginal acute services where you are trying to prop up what is really an unsustainable rota'.
"So we would expect to see a bit of a glut of those kinds of decisions going forward because our guys have been specifically asked to identify them."
Mr Hopson continued: "We have now reached the point where we cannot do everything - we cannot provide the required quality of service to the required performance standards for the money available.
"What you can't do is ask us to do the impossible and then beat us up when we fail to deliver it."
He said that "NHS leaders must agree what is going to give", adding: "Is it about reducing the size of the workforce? Is it about rationing access to care? Is it about letting waiting times slip? Is it about letting the deficits go up?"
A spokesman for NHS Improvement said: "It is an essential part of the planning process for local areas to identify which services could be unsafe, underused or unsustainable.
"It is absolutely right that decisions on the future of health services are taken locally in consultation with the people who use those services. That planning process is still going on and no decisions have been taken."
A Department of Health spokesman said: "We have given the NHS the money it has asked for in its own plan for the future - an extra £10bn per year by 2020, including almost £4bn extra this year, and we're helping hospitals by clamping down on expensive agency staff and identifying inefficiencies.
"We expect the NHS to focus on balancing the books whilst continuing to provide high-quality care for patients."
The comments come as a new NHS Providers' survey of 84 NHS Trust and Foundation Trust finance directors found that while many were optimistic about the first three months of the financial year, 38% say they are not confident they will meet financial targets set by regulators this year.
Commenting on the NHS Providers' survey, shadow health secretary Diane Abbott said: "This is an indictment of Tory underfunding and mismanagement, with four out of 10 NHS Trust finance directors saying their current performance and financial position are unsustainable.
"The Government should properly fund the NHS and address the real waste of PFI, a ballooning agency staffing bill and overcharging by Big Pharma."