The quality of care for patients could suffer as the NHS struggles to make £20bn in efficiency savings, finance directors have said.
Two-fifths of NHS finance directors expect patient care to worsen over the coming years, according to a survey.
Almost two-thirds think that the NHS as a whole will struggle to achieve the £20bn "productivity challenge" by
2015, according to The King's Fund research.
Financial directors are confident they will end this year in surplus or break even, but monetary pressures will start to bite next year, the research suggests, as the two year public sector pay freeze comes to an end in April.
The report stated that an average staff pay increase of 1% would add around £400 to £500 million to NHS expenditure.
Professor John Appleby, chief economist at The King's Fund said: "The NHS continues to perform well in the second year of the productivity challenge.
"But there are signs that future years will be harder.
"The end of the public sector pay freeze next April may add to financial pressures and increase the strain on services.
"The difficulty for local providers will be finding ways to absorb these costs without compromising the quality of care for patients."
The survey of 45 NHS finance directors, who work across the sector, also indicated that there is growing pressure on emergency care.
The number of patients who are waiting for more than four hours in accident and emergency is at its highest level in the three month period from April to July since 2004/05, the researchers found.
They also noted an upward trend in the number of patients forced to wait more than four hours before they are admitted to hospital after presenting at accident and emergency.
The number of staff was also affected.
There has been a reduction of 27,000 full-time jobs since March 2010, according to preliminary staff figures.
There are 4,800 fewer nurses and 18% of managers have lost their jobs, the data suggests, while the number of consultants has risen by 10% since 2009.
Health Minister Lord Howe said: "The NHS is on track to achieve its up-to-£20 billion savings target. The NHS made good progress delivering £5.8 billion of savings in 2011/12 while improving care for patients - waiting times have been kept low, infections have been reduced, there are more doctors, more diagnostic tests and more planned operations.
"Latest figures show that on average patients waited only 51 minutes for treatment in A and E. Patients are spending longer in A and E, but they are not left untreated during this time."