Shortened training for qualified doctors could compromise patient care and safety claims doctors.
The British Medical Association (BMA) has called for a "pause" in policy development while safety concerns are addressed and said any changes should be piloted in small studies before being rolled out more widely.
The Royal College of Physicians has also raised concerns, saying shortening doctors' training would "compromise both quality of patient care and patient safety".
Niall Dickson, the GMC's chief executive, said: "The independent review was established by the four governments of the UK to look at the changing needs of patients and the type of doctors that will be needed to provide high quality care in the future.
"There are recommendations made in the review that could require changes to postgraduate training and everyone accepts that more work needs to be done to understand the benefits and impact of such changes."
He added: "It is highly unlikely that there will be agreement about all of the issues but it is clear that work will be undertaken to look at the key issues."