Leading GPs have expressed concern over the number of family doctors in training who are already considering leaving the profession.
A new poll by the GP magazine Pulse found that around one in five trainee GPs say they expect to have left UK general practice within five years of completing training.
The survey of 310 training GPs found that 14% of trainees see themselves working abroad within five years of qualification, while 2% believe they will have left the field of medicine.
A further 2% said they see themselves in other, non-GP, roles and 1% said they believed they would change their speciality.
The Royal College of GPs said the prospect of losing so many training family doctors would be disastrous for the NHS.
Pulse said there have been reports of a number of GP trainees moving abroad following the junior doctors contract dispute last year.
It said a number of respondents to the survey said they were considering leaving the country to work in Australia, New Zealand or Canada.
The magazine said the figures undermine the Government's attempts to increase the GP workforce by 5,000 by 2020.
Commenting on the survey, Professor Helen Stokes-Lampard, chairwoman of the Royal College of GPs, said: "This is really concerning and very sad. We cannot - and must not - allow this 'brain drain' of future GPs to be lost to our profession and to future generations of patients.
"We are already having difficulties attracting medical students into GP training, but the prospect of losing new GPs so early in their careers will be disastrous for patient care and the NHS.
"Unfortunately, trainees are seeing at first hand the enormous pressures that today's GPs are facing. Yet, if properly resourced, being a GP can be the best job in the world, with endless career opportunities.
"After a decade of under-investment, we urgently need to turn general practice around and make it the attractive career option that it once was.
"The GP Forward View launched by NHS England could be the lifeline that general practice needs - but our annual assessment of its progress shows that things are not moving as quickly as they could in certain areas.
"We urgently need a properly funded family doctor service - including thousands more doctors and members of the wider practice team - so that we can attract the numbers we need into GP training, and then make it worthwhile for our hugely bright and talented new GPs to stay in family medicine for the rest of their working lives."
Dr Krishna Kasaraneni, of the British Medical Association's GP committee, told Pulse: "It is a reflection of the huge pressures bearing down on general practice that so many GP trainees, despite being at the start of their careers, are already considering quitting the profession.
"Medical graduates want to be GPs so they can treat patients, but increasingly they are struggling to provide even basic care in a climate of rising workload, stagnating budgets and widespread staff shortages.
"Despite constant promises from the Government, there is little sign that the promised extra resources for frontline patient services are emerging."
A Department of Health spokesman said: "Our view is clear - GPs are the absolute bedrock of the health service, so we're investing an extra £2.4 billion into general practice.
"What's more, we have the highest number of GPs in training ever, have agreed a pay rise, cut red tape and we're bringing in new schemes to help GPs work more flexibly."