The Government's pledge to increase the number of GPs by 5,000 by 2020 is "wholly unrealistic", medics have said.
Fresh analysis conducted by GP magazine Pulse has concluded that the family doctor workforce will increase by 2,100 "in the best case scenario".
At the current rate, there will be around 12,800 GPs entering the system by 2020, Pulse said. But thousands of doctors are planning to move abroad or retire.
The magazine said that around 700 GPs are applying for certificates to work abroad every year - so over five years this could lead to 3,500 GPs leaving British practices.
And around 7,200 plan to retire over five years, it said, after extrapolating figures from the NHS Business Authority which show that around 1,400 GPs in England retired in 2014.
"The political pledge to recruit 5,000 GPs by 2020 is wholly unrealistic," said Dr Krishna Kasaraneni, chairman of the British Medical Association's (BMA) General Practitioners Committee subcommittee on education, training and workforce.
He told the magazine: "Pulse's data analysis shows how short we are likely to be.
"We actually need a lot more GPs than this arbitrarily chosen figure to maintain a basic level of service to patients.
"With 600 GP trainee posts left unfilled last year and large sections of the workforce telling the BMA they intend to retire, there is little chance the Government will get anywhere near this target."
But a Department of Health spokesman told the magazine: "Pulse's figures don't take the whole picture into account. NHS England and Health Education England are working closely with the BMA and RCGP on a 10-point plan which sets out exactly how we will achieve this. We have been clear that our target includes registrars."
Pulse editor Nigel Praities said: "Our analysis shows that ministers should be very worried about their election pledge to recruit 5,000 GPs by the end of this parliament. They need to step up their efforts to make general practice a more attractive career, and soon."