Many of the country's doctors are trained in London
A revamp of the NHS workforce in London could cause "irrevocable damage" to medics' careers, doctors say.
The capital's health bosses want to see half of medics working in the community - double the proportion currently.
The move is linked to the roll out of the network of polyclinics in London and will see doctors spending more of their training outside hospitals.
But the British Medical Association said polyclinics were still an unproven model of healthcare.
NHS London, the regional body that oversees NHS trusts in the capital, is looking to invest an extra £132m in training over the next decade.
It is also planning to increase its workforce of nurses, midwives and doctors by 4,000 to 19,000.
However, in the future these health staff will be spending much more time in the community rather than hospitals.
NHS London's workforce strategy proposed 47% of doctors should be based in the community within 10 years - up from 25% at the moment.
A similar shift will be seen among nurses.
It is envisaged many of these staff will be working in the 150 polyclinics - super GP surgeries housing a range of staff including physios, nurses and hospital doctors - due to be set up in London.
Hospital consultants will also be expected to run outreach clinics.
To achieve this, a major reform of training is needed. Junior doctors currently spend about 90% of their time in hospitals, but NHS London said this will change if the vision is to be realised.
NHS London chief executive Ruth Carnall said said the plans were about getting "the right health professional working in the right place".
"In the future, doctors and other health staff will be spending more of their time training where they will be working - the community."
The changes in London are part of a wider reform of the NHS with polyclinics being set up across England - albeit not quite on the scale of London.
However, what happens in regards to training in London has a huge knock-on effect on the rest of the country as about a third of the medical workforce comes through the capital's training system.
A spokesman for the British Medical Association accused NHS bosses and the government were "running ahead with wholesale changes".
"Polyclinics need to bed in before changes to training. The concern is that a lot of doctors' careers could be irrevocably damaged in a system which is not yet proven."