Pontypridd MP and potential Labour leadership challenger Owen Smith has said the party is in danger of "splitting apart".
Mr Smith said he would do anything to serve the party but he and Unite union leader Len McClusky urged members to give Jeremy Corbyn more time.
Mr Smith said he had been talking to Mr McCluskey and Mr Corbyn to "explore what I can do" to heal party rifts.
He added that he has been reassured talks had been "productive".
Mr Corbyn has faced a challenge to his authority as Labour leader after he lost a no-confidence vote and many of his shadow cabinet members, including Mr Smith, resigned.
Mr Smith said he needed more time to reach a resolution over this weekend.
"Over the last week, I have been contacted by hundreds of Labour members and MPs deeply worried that the Labour Party is truly in danger of splitting apart," he said in statement.
"I share those fears and call on everyone in our movement to do all we can to avert such a disastrous outcome.
"I stand ready to do anything I can to save and serve the party.
Mr Smith said he "spoke directly" Mr McCluskey of Unite and Mr Corbyn on Wednesday "to explore what I can do to try and heal the rifts that have opened up in our movement".
He said: "On behalf of the trades unions, Len has reassured me that the talks he has opened up between Jeremy and Tom Watson have been productive and has asked that they are given more time this weekend to see what further progress can be made towards a resolution.
"Jeremy has also reassured me that he is engaging in talks with an open mind.
"I believe that all of us whose priority is to restore unity in the Labour movement and give us a chance to defeat our only true enemy, the Tories, should give these talks every chance to succeed.
"That is what I intend to do and I urge all my colleagues to do likewise."
Mr Corbyn has resisted calls to step down after Labour MPs voted by 172-40 that they had no confidence in him.
After the mass resignation of most of Mr Corbyn's frontbench team, Mr Smith and former shadow business secretary Angela Eagle were understood to be considering a formal challenge to his position.