Patients could be forced to wait weeks to see their family doctor as overstretched medics struggle to keep waiting times down during the busy winter period, Britain's leading GP has said.
In an interview with the Press Association, Helen Stokes-Lampard, chairwoman of the Royal College of GPs, said extended waiting times can pose a "serious risk" to patients.
She said some patients are already waiting two or three weeks to see GPs for non-urgent matters such as suspect lumps or bleeding problems.
But if they are forced to wait three to four weeks "the non-urgent stuff may be becoming urgent", she warned.
Dr Stokes-Lampard said she was "profoundly concerned" about how general practice will cope over the busy winter period - with particular worries about patients with long-term diseases.
If management of patients with chronic diseases is delayed so GPs can "firefight" the urgent patients then the consequences could be "very serious indeed", she added.
Winter woes have been a long-standing problem in the NHS with a lot of concern about hospital care.
But Dr Stokes-Lampard, a GP in Lichfield, Staffordshire, said every peak in workload in A&E departments is magnified at GP surgeries which are "already skating on thin ice".
Asked if people with non-urgent needs would be forced to wait weeks to see their GP, she replied: "Absolutely.
"If you've suddenly developed a lump, or you've got a funny pain somewhere, you know it's not desperately urgent for you to see your GP today but you'd like to see a GP within a few days, you'd certainly like to see them within a week to 10 days because actually you're worried.
"If it's already taking some patients two to three weeks to get in to see a GP for the non-urgent stuff, then by the time three to four weeks has passed the non-urgent stuff may be becoming urgent.
"With lumps or bleeding problems or things that could be signs of serious disease, my profound concern is that people will delay seeking help for things that could potentially be life-threatening or life-changing if they are not tackled swiftly.
"Extended waiting times pose a serious risk because of all those unintended consequences."
Asked if she was worried how general practice will cope over the winter, Dr Stokes-Lampard added: "Yes, I am concerned, I am profoundly concerned.
"It's not just A&E that sees peaks in workload. Every peak that you see in A&E is magnified in primary care just through the scale.
"As a service that is already skating on thin ice - a service that is stretched incredibly thinly - something has to give.
"Well, what do you do? If you've got to deal with people who are acutely sick on the day because people need help then chronic disease management will disappear.
"Now chronic disease management is the most phenomenal success story of the NHS - every day tens of thousands of people do not die who would have died 20 to 30 years ago because we are quietly saving them from having heart attacks, we are saving them from having strokes, we are saving them from complications of diabetes.
"And it's the biggest unsung celebration of the UK healthcare system - how much preventative medicine goes on and how amazingly good we are at saving lives.
"My worry, the big fear, is that GPs and other healthcare professionals working in the community ... if we rein back on all that preventative care and all that chronic disease management because we are too busy firefighting the urgent stuff, the knock-on consequences could take years to manifest but they will be very serious indeed. And that would be a tragedy."
She added: "(We) have got a service already stretched desperately thin that doesn't have the numbers or the scale for any resilience - we have mopped up all our resilience already - what you're left with is goodwill and professionalism being all that's left holding it together."
Labour's shadow health minister, Julie Cooper, said: "These developments are extremely worrying.
"The Government needs to wake up to the fact that there is a full-scale crisis in the NHS at every level.
"We have heard a lot about the shortage of beds and waiting times in accident and emergency departments but there has been little acknowledgement of the pressures facing GP surgeries.
"The truth is that they are overwhelmed by ever-increasing demand. Add to this a chronic shortage of GPs and a crisis in recruitment and the result is a service that is at breaking point.
"If the Government really cares about the NHS and patient safety they must listen to the words of the medical professionals because when it comes to patient health and well-being, they are the experts and ministers ignore their advice at our peril."
An NHS England spokesman said: "Of course over the Christmas and New Year period the top priority has to be medical emergencies, but the RCGP are right to remind everyone of what they describe as the 'most phenomenal success story of the NHS - every day tens of thousands of people do not die who would have died 20 to 30 years ago because we are quietly saving them from having heart attacks, strokes, and complications of diabetes'.
"That's why GP services are on track to receive an extra £2.4 billion in real terms investment by 2020 to build on this track record of success and expand access to convenient appointments throughout the week."