Mr Miliband has long been considered a future Labour leader David Miliband is due to address the Labour Party conference later, after narrowly losing the leadership to his younger brother Ed.
Mr Miliband, long considered the favourite for the top job, will attend a question and answer session in his role as shadow foreign secretary.
He has not said whether he will accept a job in his brother’s shadow cabinet – saying on Saturday it was “Ed’s day”.
But there is speculation he may be offered the shadow chancellor’s role.
The current shadow chancellor, Alistair Darling, who is stepping down from the front bench, is due to make a speech later in which he will defend his original plans to halve the budget deficit over four years.
The new leader has described the plans as “broadly the right starting point” but said he wanted to look at how they could be improved.
Nominations have opened for the 19 shadow cabinet posts which are elected by a ballot of MPs, but David Miliband and other leadership candidates are expected to take prominent jobs.
Mr Miliband, who remains shadow foreign secretary until the elections, will speak to delegates in a question and answer session on foreign affairs at the Labour Party conference in Manchester.
On Sunday he ducked questions about his future, saying it was “not a day to take anything away from what Ed is doing”.
“This conference is not about jobs for me, this is about a new future for the Labour Party,” he said.
BBC political editor Nick Robinson says a friend of David Miliband has told him that the defeated leadership contender is contemplating not running for the shadow cabinet. But Labour colleagues insist he has yet to make up his mind.
Ed Miliband has praised his brother’s “generosity and graciousness”, adding: “I think he needs time to think about the contribution he can make – I think he can make a very big contribution to British politics.”
Although David won a higher percentage of votes from Labour MPs, MEPs and party members, Ed Miliband’s success with trade union members and affiliated societies pushed him into first place.
He defeated his brother in the e leadership race by just over 1% from his brother after second, third and fourth preference votes came into play.
Ed Balls was third, Andy Burnham fourth and Diane Abbott last in the ballot of MPs, members and trade unionists.
The party has revealed that nearly a tenth of the votes cast – more than 36,000 out of 375,000 – were spoiled.
A spokesman said many voters had failed to comply with “clear” instructions to tick a box confirming they were Labour supporters.
Ed Miliband has been portrayed as being to the left of his brother and been dubbed “Red Ed” by some newspapers. But he rejected the tag as “rubbish” in a BBC interview on Sunday and said his leadership would not see “a lurch to the left”.
Mr Miliband told a fringe meeting at the conference that people had joined the party at the rate of one a minute since he was elected.
Shadow cabinet candidates have until Wednesday to put their names into the ring, with about 50 already in the running for the 19 slots up for grabs. The other members of the shadow cabinet – party leader, deputy leader, chairman of the Parliamentary Labour and the chief whip – are voted in separately.
The vote takes place until 7 October. The 19 successful candidates will then be allocated posts in the shadow cabinet by the new party leader.
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