Ed Miliband will be "fighting hard" when he returns to Parliament after taking paternity leave, shadow home affairs spokesman Ed Balls said.
Mr Balls said the Labour leader had been working on a speech to the National Policy Forum (NPF), the body responsible for the party's policy development, for the "last couple of weeks".
Mr Miliband's two-week absence after the birth of his second son Samuel has coincided with reports of infighting among Gordon Brown's Cabinet in the run up to the general election.
Political historians Anthony Seldon and Guy Lodge have suggested in their book Brown At 10 - serialised in the Daily Mail - that Labour deputy leader Harriet Harman held a secret meeting on New Year's Eve for "key plotters" to discuss how to remove Mr Brown.
Mr Balls, a key aide of the former PM, dismissed the report as "rumours" and said he did not meet with Ms Harman on December 31 last year.
He told BBC1's Andrew Marr Show: "I was at home on our New Year's Eve with friends who weren't in the Cabinet. For some reason I don't get invited to these dinners, I don't know why.
"There have always been these rumours. Fundamentally, the Labour Party, the MPs and actually the country said: 'We don't want a change of Prime Minister, we want a Labour Party which is going to stand up against an Opposition party which was going to propose in the general election campaign a VAT rise and spending cuts'.
"That should have been our priority, that was my priority and I think it was actually the priority of the vast majority of Labour Party members, I hope Cabinet members too."
Mr Balls added: "Ed Miliband and I were both shoulder to shoulder with the Prime Minister.
"And throughout that whole period, Labour Party members and MPs and the public were saying: 'Try and win that general election'. That's what I was trying to do."