The Government could push ahead with imposing a new contract on junior doctors if agreement cannot be reached in the next few weeks.
The British Medical Association (BMA) has announced its intention to go ahead with a strike on February 10 after talks broke down in the bitter dispute over pay and conditions.
The main sticking point remains weekend pay and the point at which a premium rate of pay kicks in for junior doctors.
In a letter to Health Secretary Jeremy Hunt, Sir David Dalton - who has been drafted in to broker a deal - said there was no point to future negotiations unless the BMA signalled its willingness to shift its position on Saturday rates of pay.
He said agreement must be reached by mid-February to give time to implement the new contract.
Currently, 7pm to 7am Monday to Friday and the whole of Saturday and Sunday attract a premium rate of pay for junior doctors.
An offer from the Government in November said doctors would receive time and a half for any hours worked Monday to Sunday between 10pm and 7am, and time and a third for any hours worked between 7pm and 10pm on Saturdays and 7am and 10pm on Sundays.
But in a new offer, dated January 16, Sir David said that, as part of an overall agreement, a premium rate of pay could kick in from 5pm on Saturdays rather than 7pm.
Furthermore, premium pay could start at 9pm Monday to Friday.
In his letter to Mr Hunt, Sir David said: "The BMA re-stated that they would not negotiate on this issue - and would not concede to any plain time (normal pay) working on Saturdays."
He said he was hoping to continue talks with the BMA but added: "I do not believe negotiations should restart unless the BMA state beforehand that they will negotiate on the principal outstanding issues."
He continued: "Should the BMA confirm that they will not negotiate and compromise on weekday and weekend plain time/unsocial hours then I will have to conclude that there is no opportunity for a negotiated settlement, and I would then need to advise you accordingly.
"Specifically, if effective implementation is to be assured for junior doctors then agreement is required by no later than mid-February."
Earlier, the BMA said the talks had "foundered following the Government's continued refusal to put reason before politics in agreeing a fair solution".
A full walkout has been scrapped but thousands of operations, procedures and appointments will still need to be cancelled.
Junior doctors will provide emergency care only from 8am on Wednesday February 10 to 8am on Thursday February 11.
Dr Johann Malawana, chairman of the BMA's junior doctor committee, welcomed the involvement of Sir David but said an agreement could still not be reached.
He said Sir David's "understanding of the realities of a health service buckling under mounting pressures and commitment to reaching a fair agreement has resulted in good progress on a number of issues".
He added: "It is therefore particularly frustrating that the Government is still digging in its heels.
"The Government's position - based on ideology rather than reason - risks souring relations with an entire generation of junior doctors, the very doctors who the Secretary of State has acknowledged as the backbone of the NHS.
"The Government's entrenched position in refusing to recognise Saturday working as unsocial hours, together with its continued threat to impose a contract so fiercely resisted by junior doctors across England, leaves us with no alternative but to continue with industrial action."
Shadow health secretary Heidi Alexander said it was "deeply disappointing" that the strike would go ahead.
"I am pleased that junior doctors will be covering emergency care services, but patients who see their operations and appointments cancelled next week deserve an apology from Jeremy Hunt," she said.
A No 10 spokesman said: "Clearly it is regrettable that the BMA has decided to proceed with further unnecessary industrial action.
"We will continue to stay at the table, to stay talking, to try and reach an agreement."