A series of high profile Labour politicians have now raised the prospect of a permanent split in the party, with Owen Smith the latest to add his name to the list.
Pontypridd MP Owen Smith said that the party is in danger of "splitting apart", adding that unity is needed.
"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."
Meanwhile, a source close to Angela Eagle, another possible leadership contender, refused to rule out a potential split in the party if a resolution was not made.
That comes after Lord John Prescott said Labour party could split into two groups as leader Jeremy Corbyn continues to face calls to resign from his own MPs.
Labour has found itself in turmoil after Corbyn lost the confidence of most of the Parliamentary Labour Party amid speculation he would not be able to win a potentially close general election and lead a lacklustre EU referendum campaign.
For his part, Corbyn has said he remains committed to leading the party and wants it to unite. Critics say he is not able to bring the party together.
Smith has put off his decision on running to challenge leader until after the weekend, while Eagle is said to still be ready to make a challenge but is looking for Corbyn to step down and avoid a leadership election.