Jeremy Corbyn will continue to draw up his shadow ministerial team after a difficult meeting with MPs and peers that saw him face "hostile" questions.
Labour's new leader is also heading to Brighton to address the TUC congress where he will underline his support for the campaign to halt tough new strike laws.
The speech is likely to be met with a more enthusiastic reception than his first appearance in the new job to the Parliamentary Labour Party, which was greeted with silence rather than the table thumping a newly elected leader traditionally enjoys.
Mr Corbyn told the group his top priorities are housing, next year's elections in Scotland and Wales, and winning the general election in 2020.
Shadow foreign secretary Hilary Benn had earlier attempted to calm fears among many Labour MPs that Ed Miliband's successor could campaign for Britain to leave the EU in the in/out referendum expected next year, insisting Mr Corbyn had told him "we will stay to fight together for a better Europe".
But, addressing the PLP, the Opposition leader left the door open for Labour to campaign to leave the European Union, insisting the party "can't just give (David) Cameron a blank cheque".
Shadow business secretary Angela Eagle said it was too early to say how the party would campaign.
She told BBC 2's Newsnight: "That has got to be the aim but we are not going to, before we even know what the Prime Minister is going to come back with, know precisely how we are going to be campaigning."
Ms Eagle added: "What we have got to recognise is that politics is dynamic and there is a lot of change going on in Europe at the moment."
The scale of the problems Mr Corbyn faces in uniting the party were underlined as key members of his new team gave his leadership a lukewarm response.
Shadow education secretary Lucy Powell, said taking the job had been a "difficult" decision and admitted she did not believe Mr Corbyn and shadow chancellor John McDonnell would be able to convince voters where the previous leader failed.
Mr Benn declined to offer his full endorsement over the controversial appointment of Mr McDonnell, who boasts in his Who's Who entry that his hobbies include "fermenting (sic) the overthrow of capitalism", in the crucial economic role.
Mr Corbyn will announce the rest of his shadow ministerial team in the next few days although the party is unable to say when the list will be finalised.
The Islington North MP accused critics of "living in the 18th century" amid jibes that he overlooked women for Labour's biggest jobs, insisting he did not regard the traditional Treasury, home affairs and foreign affairs briefs as the most important.
In total, 16 posts in Mr Corbyn's senior team have gone to women, with 15 filled by men.
Mr Corbyn will face his first Prime Minister's Questions tomorrow and has received more than 33,000 responses to his request for question suggestions.