Video report by ITV News Correspondent Romilly Weeks
Jess Phillips has pulled out of the Labour leadership race after failing to gain enough support to progress further in the contest.
The Birmingham Yardley MP was unable to win backing from any unions, of which she would have needed at least two - plus a Labour affiliate - or from at least 33 Constituency Labour Parties (CLP).
But one candidate who began the race as an underdog - Lisa Nandy - received a major boost hours later when industrial union GMB endorsed her for leader.
Ms Nandy said she "could not be more proud" to win the support of GMB, which has edged her closer to the final ballot.
Ms Phillips, in a statement announcing her decision to quit, said the party needs a candidate that can unite all parts of the movement and "I have to be honest that at this time, that person isn't me".
She also released a video message on social media announcing she was quitting, but she did not endorse another candidate, despite earlier signalling she would support Ms Nandy.
GMB's General secretary Tim Roache said he was "proud" to nominate Ms Nandy and claimed "the more members see of Lisa in this contest the more impressed they will be by her ambition, optimism and decisive leadership".
The union also endorsed Angela Rayner for deputy leader.
Shadow Brexit secretary Sir Keir Starmer is already through to the contest's final stage and will have his name on the ballot, but the three remaining candidates are still competing for support.
Shadow business secretary Rebecca Long-Bailey, shadow foreign secretary Emily Thornberry and former shadow cabinet minister Lisa Nandy - as well as Sir Keir - were all vying for endorsement at the GMB hustings in London.
Ms Phillips and Ms Thornberry only just scraped through the competition's first stage after gaining 23 nominations from colleagues - just one above the threshold.
In comparison, the race's favourite Sir Keir had support from 88 Labour party colleagues.
He is expected to be joined on the final ballot by Ms Long-Bailey, who has support from the left of Labour, and Lisa Nandy, who is seen to represent the party's centre ground.
It is not clear at this stage however whether Ms Thornberry will eventually win enough support to progress - but she believes she can.
When leaving the GMB hustings she was asked if she is confident about being on the final ballot. "Of course, of course", she responded.
ITV News Political Correspondent Romilly Weeks explains the latest Labour developments:
After nominating its prospective leader and deputy, GMB shared a pair of edited photos which showed Ms Nandy as a Game of Thrones character and Ms Rayner as a Hunger Games character.
The candidates have until February 14 to lobby CLPs, unions and affiliates for support, before the final decision is passed to Labour supporters.
Labour members, registered supporters and affiliated supporters will have from February 21 to April 2 to elect a new leader, which will be announced on April 4.
Earlier in the contest Ms Phillips appeared on the Calling Peston podcast, in which she revealed she would support Ms Nandy if she herself was not in the race.
But ITV News Political Correspondent Paul Brand understands Ms Phillips will in fact support Sir Keir.
In the podcast Ms Phillips said she would happily serve in any of the candidate's prospective shadow cabinets and said her preferred role would be Home Secretary.
Had Ms Phillips made it to the final ballot it is not likely she would have had much support from Labour members who joined in their thousands to elect Jeremy Corbyn in 2015.
But it is thought dozens of Ms Phillips social media followers - of which she has 357,000 - may have joined the party in order to support her on the final ballot.
With their favourite candidate out the contest it is likely many of Ms Phillips' supporters will back Sir Keir or Ms Nandy - dealing a blow to Ms Long-Bailey, who will be relying on the Corbyn-supporting membership.
Ms Thornberry said she was "very sorry" that Ms Phillips had pulled out of the contest, arguing that favourites Sir Keir and Ms Long-Bailey needed to face a challenge.
She said: "We need to broaden our debate, not narrow it, and force the two favourites to prove they're up to the fight by pitting them against some real strength.
"Jess is a sad loss in that effort, but we will keep going."
Ms Nandy also said she was sorry that Ms Phillips had dropped out, adding: "She has made waves, shown great friendship and I'll miss her in this contest."