The UK government is pressing the European Commission to review the rules on how long junior doctors can work.
The new rules come into effect in August
From August, junior doctors will not be allowed to work more than 58 hours a week in line with a European directive.
However, recent court rulings have suggested that time "on call" must be counted as time worked.
Health Secretary John Reid has written to the European Commission warning that such a policy could have "a severe impact" on the NHS.
Under the terms of the directive, trusts that fail to cut the number of hours their doctors in training work face fines and the threat of employment tribunals.
The Department of Health has urged hospitals to do all they can to meet the new rules.
This includes transferring some of the roles and responsibilities of juniors doctors to other staff, including nurses.
European Commissioner Stavros Dimas said he would bring forward legislative proposals to resolve the problem before the summer.
He said he was aware that the directive and the recent court rulings raised "practical difficulties" for the health sector.
However, the Department of Health has acknowledged that even if new rules are agreed they are unlikely to be in place by August.
The British Medical Association said the changes could be at least two years away.
"The NHS has to be prepared for significant change," said Dr Simon Eccles, chairman of its junior doctors committee.
"The Working Time Directive is essential health and safety legislation - patients should not be treated by tired, overworked doctors.
"We would like to see the government preparing for the changes rather than investing all its energy in trying to get around them."
Dr Eccles said "on call" should be counted as time worked.
"A brief period of rest in a hospital on-call room, knowing you could be interrupted at any minute, is not the same as being at home."