The NHS could reach "breaking point" within the next few years due to increasing demands on the service, senior doctors said.
Financial pressures may mean junior doctors are not given training posts within the NHS and the overall number of places at medical school could drop.
This is despite extra burdens on the health service, including limits on how many hours doctors can work, more hospital admissions and people living longer than ever before, according to the study from the UK Royal Colleges of Physicians (RCP).
Those specialties dedicated to looking after very ill people are facing particular strain, it said.
Dr Andrew Goddard, RCP director of medical workforce, said the combination of factors was "adding further stress to a system which may reach breaking point within the next few years".
In 2009, the number of consultant posts created across the UK increased by 10.2%.
However, financial pressures on the NHS means that rise may not continue and there are "growing fears" of a lack of training posts for young doctors.
Dr Goddard said: "We have already seen a drop in the number of new posts being advertised in 2010, and although we have enough doctors in training to develop a consultant-delivered NHS, these doctors need to have jobs to go into if this service is to be realised."
The latest study comes after the RCP in England warned last week of patients being left in the hands of junior doctors because of inadequate consultant cover on weekends.
It is calling on hospitals to ensure consultants are available every single day of the week for at least 12 hours per day.
