The NHS requires an increase of at least £4 billion in funding over the next two years to avoid patient care from deteriorating, according to health think tanks.
The three health think tanks - the Health Foundation, The King's Fund and the Nuffield Trust - carried out a joint analysis of NHS finances in England and say NHS funding will be at one of the lowest rates in its history without a cash injection.
Without an increase of at least £4 billion in 2018/19 patients will wait longer for treatment, more services will be rationed and quality of care will deteriorate, the organisations said.
The briefing paper, released ahead of the Budget statement on November 22, estimates that based on current spending plans there will be a funding gap of at least £20 billion by 2022/23.
Seven years of austerity in the health service, coupled with rising demand, is "taking a mounting toll on patient care", their briefing adds.
They said that the next financial year would be a "crunch year" for the NHS, with funding growth slowing to 0.4%.
This is the "the lowest rate of growth of this parliament and one of the lowest in NHS history", they added.
The health charities estimated that NHS spending would need to rise from £123.8 billion in 2017/18 to at least £153 billion in 2022/23 - a 4.3% average annual increase - to keep pace with demographic pressures and increasing costs.
They called on the Government to increase NHS spending in real terms for every year of the parliament.
The organisations also said ministers should make an "immediate, substantial down-payment on its promise to increase NHS funding by £8 billion by the end of the parliament".
Meanwhile, any increase in pay for NHS staff should be fully funded, rather than coming from the existing settlement, they said.
"After seven years of austerity, the dramatic improvements made in health care over the last 20 years are at risk of slipping away." said Chris Ham, chief executive of The King's Fund.
"The message is clear - unless the government finds the money the NHS and social care need, patients, service-users and their families will suffer the consequences."
Yesterday, the body's chief executive Chris Hopson said that last year NHS England missed all four major targets - the four-hour A&E standard, the 18-week elective surgery waiting time standard, the expectation that cancer patients will begin treatment within 62 days and the ambulance response time target.
Health Secretary Jeremy Hunt and NHS England chief executive Simon Stevens will speak at the NHS Providers conference on Wednesday.