Labour’s election result should not be seen as a “famous victory” and was “not good enough”, says former shadow chancellor Chris Leslie.
The Labour MP, who has been a critic of leader Jeremy Corbyn, said he recognised the party ran an “effective campaign” but a Conservative prime minister currently sits in No 10.
Questions should be asked about how the party can win a majority, he added.
The Tories have said they will form a government with the support of the DUP.
Speaking on BBC Radio 4’s Today programme, Mr Leslie said: “We shouldn’t pretend that this is a famous victory. It’s good as far as it’s gone, but it’s not going to be good enough.”
Labour secured 262 seats in the election and boosted its vote share to 40%.
The Conservatives won 318 seats – eight less than it needed in order to secure a majority.
Mr Leslie said Labour missed an “open goal” as he had “never known” a more beatable prime minister than Theresa May.
He believes his party still has “more to do” and needs to learn lessons so it can go on to win a majority.
The Labour MP for Nottingham East refused to say whether he thought Mr Corbyn was credible prime minister.
“I will never apologise for my view which is, yes of course you’ve got to inspire people, and we haven’t done that well enough in the past.
“But you’ve got to convince them of your credibility and that you can move from protesting about the government to being in government.”
Mr Leslie said Labour MPs were “working in this together” but he would not commit to serving in a shadow cabinet.
He said he feared an issue would arise which would go against his principles and he would have to resign.
“I’m never going to give in arguing for what I believe is a pathway to a majority Labour government,” he added.