The NHS is facing "mission impossible" to deliver on next year's performance targets and budget savings, a leading health chief has said.
Chris Hopson, chief executive of NHS Providers, said the health service was a "can-do" organisation but many trusts believe they "can't deliver" on Government demands for the next financial year beginning next month.
An analysis by the trade association, which represents hospital, ambulance and mental health trusts, found an "unbridgeable gap" between the targets and the funding that is available, with frontline funding increases being lower than in previous years at 1.3%.
Combined with a demand to rein in "slipping" waiting time targets for accident and emergency and routine operations and a forecast rise in demand for services, Mr Hopson said: "Take all this together and it's mission impossible. The numbers don't add up."
The NHS faced huge pressure over the winter, with A&E waiting times of four hours and more reaching record levels, amid fears of a staffing crisis.
Mr Hopson estimated trusts would need £2.5 billion more to turn performance around within a year.
In a blog post on the organisation's website, Mr Hopson said: "NHS trust leaders want to meet NHS standards, achieve financial balance and improve their performance.
"But you get what you pay for. Trusts can only deliver if they get the appropriate funding and support. Without these, difficult choices are required.
"If we are to maximise the use of NHS resources, plan properly, treat staff fairly and be straight with the public.
"NHS leaders have to be realistic about what can be delivered next year.
"Trusts won't be able to recover the A&E and elective surgery targets across the whole year - the best we can hope for is turning the current performance decline into an improvement.
"Given that demand and cost increases will easily outstrip funding and efficiency increases, just reproducing this year's financial performance is a stretching target."
A Department of Health spokesperson said: "This report fails to acknowledge that the NHS has a strong plan to improve performance - backed by £2 billion for social care and £100 million for A&E announced in the Budget.
"Nor does it acknowledge the hard work of NHS staff treating more than 900,000 more people a year in A&E within four hours, or performing more than 1.9 million more operations annually than in 2010."