A new poll by the GP magazine Pulse found that about one in five trainee GPs say they expect to have left UK general practice within five years of completing training.
The survey revealed there have been reports of a number of GP trainees moving abroad following the junior doctors contract dispute last year.
The study showed a number of respondents to the survey said they were considering leaving the country to work in Australia, New Zealand or Canada.
The Royal College of GPs said the prospect of losing so many training family doctors would be disastrous for the NHS.
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.”
The survey of 310 training GPs found that 14 per cent of trainees see themselves working abroad within five years of qualification, while two per cent believe they will have left the field of medicine.
A further two per cent claimed they see themselves in other, non-GP, roles and one per cent admitted they believed they would change their speciality.
The magazine said the figures undermine the Government’s attempts to increase the GP workforce by 5,000 by 2020.
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.”
The Department of Health maintained that every effort is being made to ensure trainee GPs remain in the profession, with additional investment in services.
A spokesman said: “Our view is clear - GPs are the absolute bedrock of the health service, so we’re investing an extra £2.4bn 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.”