Four in 10 European doctors are considering leaving the UK following Britain's vote to leave the EU, research suggests.
The British Medical Association (BMA) found that 42% are considering quitting the UK, with a further 23% unsure.
These figures could spell "disaster" for the NHS, which is already facing mounting staff shortages, according to the BMA.
About 10,000 doctors who work in the NHS - 6.6% of the UK medical workforce - qualified in Europe
A survey of more than 1,000 of these doctors found that they felt "less committed" to working in the UK following the vote on June 23 last year.
Many of the doctors also felt less appreciated by the Government following the result.
The BMA said that recruiting from Europe had been vital in dealing with staff shortages in the health service.
Dr Mark Porter, chairman of council at the BMA, said: "While thousands of overseas and EU doctors work across the UK to provide the best possible care for patients, many from the EU are left feeling unwelcome and uncertain about whether they and their families will have the right to live and work in the UK after Brexit.
"These are the people who staff our hospitals and GP surgeries, look after vulnerable patients in the community and conduct vital medical research to help save lives.
"Many have dedicated years of service to healthcare in the UK, so it's extremely concerning that so many are considering leaving."
Dr Porter said an increasing number of EU doctors departing the UK would be a "disaster" and threaten high levels of quality care.
He added: "The government must act now to ensure long-term stability across the healthcare system by providing certainty to medical professionals from the EU about their future in the UK.
"It must also ensure that a future immigration system allows the NHS to continue employing EU and overseas doctors to fill staff shortages in the health service."
West Sussex GP Dr Birgit Woolley, originally from Germany, has worked in the UK for two decades.
"Since the result of the EU referendum I feel increasingly uncertain about my future here, and am considering returning to Germany," she said.
"It is unsettling that in a country that I have contributed to for 20 years and consider home, I am now seen as a foreigner and have to prove that I deserve to live and work here.
"I feel supported by my patients, with even those that voted leave telling me, 'You can stay because you're a doctor. We like you. We didn't mean you.'"