A routine seven-day doctor service is "unrealistic" and could have a serious effect on weekday care, Britain's leading GP has said.
Professor Helen Stokes-Lampard, chairwoman of the Royal College of General Practitioners (RCGP), said most GPs were working "at the limits of what is safe", with a number failing to keep pace with patient demand.
Making GPs available at the weekend would reduce the availability of doctors to provide patient care during the week, she said.
Prof Stokes-Lampard said: "GPs are working flat out to do the best they can for their patients, but with a severe shortage of family doctors already seeing record numbers of people, there is no way that a seven-day routine service could be delivered without having a serious impact on services through the week.
"Patients can always see a GP through the out-of-hours service when they urgently need one.
"But there is a distinction between 'need' and 'want' and there is very little evidence to show that patients want or need to see a GP for non-urgent care on a Sunday afternoon."
She also told the Guardian: "It's unrealistic in the current climate. We haven't got the people, we haven't got the resources."
Some 1.3 million patient consultations take place in general practice every day, with around 60 million more patients every year compared with five years ago, she estimated.
"But the number of GPs has not kept pace with patient demand and while we are seeing as many patients as we can, patient safety - and doctors' own health - must be paramount," she said.
The Government must invest in general practice so that GPs can provide a safe weekday service, she added.
Prof Stokes-Lampard's remarks came after she warned last month that 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.
If management of patients with chronic diseases is delayed so GPs can "firefight" the urgent patients, the consequences could be "very serious indeed", she said.
A Department of Health spokeswoman said: "This is a common-sense reform with wide public support - and one we will deliver.
"People don't just get ill Monday to Friday, nine to five, and 18 million patients now have weekend and extended access to a GP, which has already shown evidence of relieving pressure on other parts of the NHS.
"To deliver our pledge, we are putting an extra £2.4 billion into GP services, which will help expand the workforce."Subscribe to our Newsletter