The health secretary has misrepresented a key study used to back the case for more seven-day NHS care, the editor of the British Medical Journal says.
Dr Fiona Godlee has written to Jeremy Hunt about recent comments where, she says, he has implied the higher weekend death risk is due to poor staffing.
She says the study used to back this up - published in her journal in September - did not apportion blame.
But the government said there was enough evidence to support the claims.
The study has been repeatedly used by Mr Hunt.
He has found himself at loggerheads with the British Medical Association, which owns the BMJ, over the junior doctor and consultant contracts.
The research identified what it called a "weekend effect" in England.
It said over the year studied - 2013-14 - there had been 11,000 excess deaths from Friday to Monday.
This was based on an analysis of hospital records, which found an admission on Fridays led to a 2% increased risk of death compared with Wednesdays, on Saturdays it was 10%, on Sundays 15% and Mondays 5%.
But the study said it was not clear exactly how many of these could have been avoided as the researchers could not be sure they had fully taken into account the fact that patients admitted at weekends tended to be sicker than those admitted during the week.
It said it would be "misleading" to conclude all these deaths could have been prevented.
But it also said the findings raised "challenging questions" about weekend services that could not be ignored.
The research was carried out by seven leading doctors and statisticians, including NHS England medical director Sir Bruce Keogh.
After the study was published, Sir Bruce said the "moral and social case for action is simply unassailable".
But Dr Godlee has taken issue with comments made by Mr Hunt recently.
In the House of Commons last week, he said the seven-day changes were "about the fact that someone is 15% more likely to die if admitted on a Sunday than on a Wednesday because we do not have as many doctors in our hospitals at the weekends as we have mid-week".
Asked about the junior doctors' protest on Saturday Mr Hunt told BBC Radio 4's Today programme: "What we want is to change the balance of pay between weekdays and weekends so we don't force hospitals to roster three times less medical cover at weekends and what that leads to is a 15% increase in your chance of dying if you're admitted at weekends compared to a weekday."
In the letter to Mr Hunt, Dr Godlee says: "I am writing to register my concern about the way in which you have publicly misrepresented an academic article published in The BMJ.
"This clearly implies that you believe these excess deaths are avoidable."
Dr Godlee calls on Mr Hunt to clarify his comments.
Responding on behalf of Mr Hunt, Health Minister Ben Gummer said: "Significant independent clinical evidence shows increased mortality in our hospitals at weekends linked to reduced clinical cover.
"The BMJ authors themselves acknowledge that - and any debate about precisely how many of the thousands of deaths are avoidable misses the point.
"What all doctors want is to provide the best care for their patients, and the public rightly expect the highest standards whichever day of the week they are admitted to hospital - the government is committed to supporting that."