Margaret Beckett has publicly warned environment secretary David Miliband against running for the Labour leadership.
In an interview with the Daily Telegraph, the foreign affairs secretary said she felt the 41-year-old MP would be a "poor bloody human sacrifice" if he were to stand against the bookie's favourite to succeed Tony Blair, chancellor Gordon Brown.
Describing Mr Brown as "head and shoulders" above the handful of others who have announced they will run for the leadership, Ms Beckett praised Mr Miliband's parliamentary performance to date but could not recommend him to run.
"He is very bright. He is a very good minister. I am sure he will be a major figure in the party for a long time to come and a major contender at some time in the future," she told the newspaper.
"But should he take this step to satisfy somebody else's prejudices? He would be daft."
Currently only two MPs, the left-leaning Michael Meacher and John McDonnell, have declared they will run for the leadership when Mr Blair steps down after a decade in charge.
However the foreign secretary argued that the leadership race would be a waste of time and money.
She commented: "If Gordon fell under a bus tomorrow we have got a lot of potential leaders, but it is no discredit to any of them to say that Gordon is head and shoulders ahead of those, so what is the point of having an artificial contest for the sake of it?"