Almost two thirds of finance directors at NHS trusts believe the quality of patient care has deteriorated in the past year.
A new report from the influential King's Fund think-tank found worsening patient care and a health service under pressure due to financial problems.
Its detailed review of 2015/16 found 67% of NHS trusts ended the financial year in deficit, including 86% of acute hospitals.
More than half of finance directors expect their trust to end the next financial year in deficit, too, and are "very pessimistic", the report said.
The study included the views of 87 NHS trust finance directors, plus 42 finance heads from 47 clinical commissioning groups (CCGs), which look after a large chunk of the NHS budget and manage local services.
Some 65% of NHS trust finance directors thought patient care had got worse over the last year, as did 54% of CCG finance leads.
These findings "are the most worrying" since the King's Fund began asking this question in 2012, the report said.
Only 2% of trust finance directors and 12% of CCG finance leads said that patient care had improved over the past 12 months.
Asked to identify their top three concerns, trust finance directors said they were most concerned about delayed transfers of care, so-called "bed blocking", which is at its highest level since 2008.
This occurs when people are medically fit to leave hospital but do not have the right care in place in the community for them to be able to go home.
Trust finance directors also expressed concern about performance against the four-hour A&E waiting times target, which is currently the worst on record.
They also said staff morale was being affected by pressures on the NHS.
Some 38% of NHS trust finance directors are currently concerned about achieving their savings plans this year.
"This is the most pessimistic finance directors have been at this time of year since our survey began," the report said.
Almost half (48%) of those trusts that received money from the Government's Sustainability and Transformation Fund, which was intended to help ease the NHS deficit, are still forecasting a deficit by the end of the year.
The report said extra cost pressures this year and next will "all but wipe out" the front-loaded money given by the Government as part of the Comprehensive Spending Review.
"It is unsurprising then that when asked about achieving financial balance in 2017/18, 64% of trust finance directors say they are very or fairly concerned."
But overall, the NHS deficit may tumble this financial year to around £1.4 billion (around £1 billion less than the previous year), the report went on.
There are also worries about being able to recruit doctors and nurses to plug shifts following the introduction of a cap on agency spending by the Government.
More than half of trusts (54%) were fairly or very concerned about their organisation being able to secure agency nursing staff at the hourly rate that has been set.
The report also confirmed that 8% of patients - more than 1.85 million - spent longer than four hours in A&E across the year, the worst performance since 2003/4.
The number of patients waiting for hospital treatment is estimated to have risen to 3.7 million, an increase of 17% (almost 500,000 patients) over the year and the highest number since 2007.
On bed blocking, at the end of March 2016 more than 5,700 patients were delayed in hospitals, an increase of 15% over the year and the highest number since 2008.
John Appleby, chief economist at the King's Fund, said: "2016/17 is a watershed year for the NHS in which it has been tasked with eradicating deficits and improving performance.
"Despite significant additional funding and a huge effort to contain deficits, it is clear that this is going to be a Herculean challenge.'
Shadow health minister Justin Madders said: "This report is a yet another reminder that Jeremy Hunt has completely lost control of NHS finances and is failing to protect patient care.
"The NHS has been plunged into the deepest financial crisis in a generation, with nine out of 10 hospitals ending the last financial year in the red.
"Instead of trying to repair hospital finances, ministers are demanding the NHS makes £22 billion of 'efficiency savings' which nobody believes can be achieved without cutting staff or closing services."
Health minister David Prior said: "As the King's Fund makes clear, this Government is investing significant additional funding in the NHS – an extra £10 billion a year by 2020, which is only possible thanks to our strong economy.
"We recognise parts of the NHS are under pressure as demand rises in large part due to our ageing population, but we are supporting the NHS's plans to deliver more care outside hospital settings and improve performance, including by reducing the use of expensive agency staff."
Katherine Murphy, chief executive of the Patients Association, said: "These figures show that the crisis in the NHS is growing by the day, with no sign of resolution. The scale of the anticipated financial deficit for trusts in England is devastating and means that local managers and clinicians are facing a meltdown in their organisations."
An NHS England spokesman said: "This report confirms that while non-elective admissions over the past year are up by 2% and inpatient bed days are stable, the final quarter of 2015-16 was particularly busy with more than two million treated in A&E in March alone. This was compounded by the effects of the delayed flu spike and we also saw the effects of delayed care and industrial action beginning to show."