Pulling out of the EU would leave the NHS facing a "real challenge", Jeremy Hunt has said in the latest intervention by a senior minister in the referrendum debate.
Writing in The Observer, the health secretary said the economic shock caused by Brexit could starve the cash-strapped health service of investment.
He also wrote that some of the 100,000 foreign EU citizens on the workforce could quit the country amid "uncertainties" over the status of visas and work permits.
His warning prompted claims of government scaremongering in the lead up to the 23 June referendum.
Matthew Elliott, chief executive of Vote Leave, argued that Brexit would release funds to improve the NHS.
"Under Jeremy Hunt's stewardship, the NHS has plummeted into a financial crisis," he said.
"If we vote to leave we can stop wasting money on EU bureaucrats and instead spend our money on our priorities like the NHS."
Mr Hunt said in his article that he believed Britain would survive economically outside the EU and would strike trade deals, but not without "years of economic uncertainty".