Education Secretary Alan Johnson has stepped aside from the race for the Labour leadership, saying he will support Chancellor Gordon Brown.
Mr Johnson had been seen as a rival to Mr Brown
Mr Johnson had been seen as a possible Blairite contender to take on Mr Brown, who is the overwhelming favourite.
The ex-postman told the BBC he intends to instead stand for deputy leader.
Ex-minister Michael Meacher signalled he may stand for leader when Tony Blair steps down next year, saying there should be a "centre left" candidate.
Mr Johnson broke the news of his decision to BBC political editor Nick Robinson, saying Mr Brown was respected throughout the party.
'Towering political figure'
"It is, of course, a matter for the party to decide who the leader's going to be, but my view is Gordon is a towering political figure," he said.
"It's not a position that I ever sought and there is a superb candidate in Gordon Brown."
He said as a deputy leader he hoped to "complement, help, cajole and assist" the party leader and occasionally tell them what they do not want to hear.
"I think that's an important role and that's one I want to put myself forward for."
Mr Johnson, the MP for Hull West and Hessle, is expected to formally announce his candidacy for the deputy job on Friday and says he has more than the required 44 supporters to be nominated.
A battle for the Labour leadership seemed certain after Mr Blair announced in September that he would leave Downing Street within a year.
But despite speculation that Mr Johnson or Home Secretary John Reid would mount a bid from the Blairite wing of the party, the odds of a heavyweight challenge to Mr Brown have lengthened.
The only other candidate to officially declare that he will run for the job is left-wing MP John McDonnell and there are some doubts about whether he can get the required number of backers.
On Thursday former environment minister Michael Meacher signalled he had still not ruled out a leadership bid.
Launching a climate change campaign he said "There should be a candidate of the centre left and it has to be someone who can give leadership".
"The environment is a challenge to the consensus and to all the candidates whoever they are"
There is a "crowded field" of applicants for John Prescott's job - candidates for the deputy post also include Peter Hain, Hilary Benn, John Cruddas and Harriet Harman.