Doctors are calling for regulators to offer guidance over whether they should help patients circumvent "shortcomings" of NHS care.
The NHS faces challenges because of a growing elderly population
A recent report highlighted moves such as having tests done privately to jump NHS waiting lists.
Doctors for Reform wants the General Medical Council to clarify whether medics should explain how patients can work the system to their advantage.
The GMC said it would be consulting on the issue later this month.
Guidance currently states that doctors must give patients "the information they want or need in a way they can understand".
Professor Karol Sikora, a leading cancer specialist and member of Doctors for Reform, said: "Does withholding of information about treatments that might be in a patient's best interest but are available only either in the private sector or abroad constitute a contravening of GMC guidance?
"We understand that this is a very difficult issue with far-reaching consequences for the NHS."
A GMC spokeswoman said: "We are reviewing our guidance on consent.
"As part of that process we are considering the question as to whether doctors should provide information about 'any treatment that you believe will be more effective for the patient than those that the organisation offers, but which is not available in the organisation providing care'.
"We will be asking for views on this issue as part of our consultation later this month which Doctors for Reform would be welcome to contribute to."
The consultation comes as doctors are calling for a debate over how the NHS should operate in the future.
Many doctors claim the NHS cannot carry on providing as many treatments as it does now, due to the growing elderly population.
Local heath chiefs are already restricting access to treatments for conditions such as hernias and varicose veins to save money.
The British Medical Association will launch its vision for what the NHS's future on Tuesday, which will look at the government's reform programme and the challenges for the future.
Dr Tim Crayford, of the Association of Directors of Public Health, said: "The country needs a public debate about what the NHS is there for, which should be underpinned by both the effectiveness and the cost-effectiveness of treatments."