Thousands of trainee medics could quit the NHS because of a shortage of training posts, doctors' leaders warn.
There are fears that more doctors could go overseas
A survey of 235 doctors for the British Medical Association found a third had not been offered a training post after their current contracts end in August.
The BMA blames rising numbers of newly qualified medics and applicants from overseas, as well as training changes.
The government said training posts had not been reduced and there were no plans to reduce training opportunities.
The BMA warns there would be a "lost tribe" whose skills would be wasted under the current situation.
Of the trainees surveyed, 60% said they might go abroad if they could not get an appropriate training job and a third said they might quit medicine altogether.
They will be able to take up non-training posts, but the BMA warns this will mean they will not be able to continue to develop their skills.
Training posts are approved by medical colleges, while non-training posts are usually set up by trusts to provide staff to fulfil service needs.
The BMA warns opting for a non-training post may mean doctors are then not able to get back on to the training programme, as more and more trainees will be competing for the house officer posts.
The issue is set to be debated at the BMA's annual conference, which begins on Sunday in Manchester.
The BMA says there are too many doctors competing for too few posts.
More doctors are coming out of medical school and there has been an increase in overseas doctors coming to the UK.
In addition, a number of training posts have been earmarked by hospitals for a new junior doctor training programme, and so are not available for doctors already in the established system.
The BMA says some of the vacancies which are available have attracted over 1,000 applications.
The association adds up to 10,000 doctors training under the existing system could face problems in two years' time when they, and the first tranche of those trained under the new system, are all seeking specialist posts.
There are currently around 49,000 junior doctors working in the UK.
Simon Eccles, chairman of the BMA's junior doctors committee, said: "It's a huge irony that the UK is short of doctors, hospitals are overstretched, and still there aren't enough training posts to go round.
"People are queuing up to study medicine, and thousands of doctors from overseas want to work in the NHS.
"It's absurd that such a huge amount of talent - which has cost millions of taxpayers' pounds to nurture - could go to waste.
"The government seems to think that doctors will be content with jobs that provide no training, but our research shows many will leave the NHS instead."
But a Department of Health spokesperson said: "There has been no reduction in the number of posts, and there is no intention to reduce training opportunities in the future.
"Training posts in the NHS should, however, continue to meet the needs of patients.
"Future entry into training will be via a fair and open competition.
"There has always been healthy competition in popular areas such as surgery and some parts of England, in particular London."