The UK's Royal College of Physicians said that financial pressures may mean junior doctors are not given training posts within the NHS, while the overall number of places at medical school could also drop.
At the same time their report said that medical services across the UK were facing extra burdens including limits on how many hours doctors can work, more hospital admissions and people living longer than ever before.
The doctors warned that services dedicated to looking after very ill people were facing particular strain.
About 3,800 NHS jobs are set to go this year across Scotland, but unions have warned that relying on staff turnover to reduce numbers means some vital staff risk not being replaced.
The latest warnings came in the annual census of members by the Federation of the Royal Colleges of Physicians (RCP) of the UK, which includes the organisations in Glasgow and Edinburgh.
Dr Andrew Goddard, RCP director of medical workforce, said factors such as reduced workforce and the rising demands for care were "adding further stress to a system which may reach breaking point within the next few years".
The number of consultant posts created across the UK has increased in recent years.
But the census, based on responses from over 4,200 doctors across the UK, warned that financial pressures on the NHS meant rises may not continue and there were "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 RCP wants hospitals to ensure consultants are available every single day of the week for at least 12 hours per day to deliver care to patients.
Sir Richard Thompson, president of the RCP, said: "Patients deserve better care at night and at weekends, delivered by consultant physicians, and this will only be achievable if we continue to increase the number of posts, particularly in acute medicine."
The latest report found that 59 per cent of consultants "often or always" had to work faster on ward rounds than the 15 minutes per patient recommended by the RCP.
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European rules limiting a doctor's working week to 48 hours are also having an effect, the RCP said, with 58 per cent of consultants doing jobs that previously would have been done by junior doctors.
Almost the same percentage said they have "little or no time" to support their trainees.
Jackie Baillie, Scottish Labour's health spokeswoman, said the colleges were right to highlight the problems being faced by the NHS.
Margaret Watt, chair of the Scotland Patients Association, said action was needed now to protect the NHS and make sure it could cope in the future.The British Medical Association (BMA) Scotland agreed that the NHS was facing serious pressures in the future, but denied that rules on working hours were to blame.
A Scottish Government spokeswoman said: "The Scottish Government has guaranteed that the quality of healthcare is our top priority.
"Despite the toughest financial climate since devolution, the NHS in Scotland will have more money and more staff by the end of this administration than it had at the beginning."