Tony Blair says Labour has gone through "profound change" and he is "not sure it is possible" the party can be “taken back” by moderates.
The former prime minister said under Jeremy Corbyn is now a “it is a different type of Labour Party” and he hopes it is not “lost”.
He hinted that a centrist party could form if, "for example, the choice at the next election is Boris Johnson versus Jeremy Corbyn".
Mr Blair told Nick Robinson's Political Thinking Podcast: "I don't know what will happen and I don't know how it will happen.
"But I just don't believe people will find that, in the country as a whole, an acceptable choice. Something will fill that vacuum."
His comments come after another leading figure of the Blair era, Lord Blunkett, warned that the party is facing “irrelevance” unless there is a rethink of the “Corbyn project”.
Mr Blair said: “I’ve been a member of the Labour Party for over 40 years. You do feel a strong loyalty and attachment, but at the same time it’s a different party. The question is, can it be taken back?”
“This is a different type of Labour Party. Can it be taken back? I don’t know.”
The former PM’s comments come after Labour activists in Enfield North passed a vote of no confidence in Joan Ryan, a minister in the Blair administration who now chairs Labour Friends of Israel.
Ms Ryan, a vocal critic of Mr Corbyn’s handling of anti-Semitism, blamed the 94-92 defeat on “Trots, Stalinists, Communists and assorted hard left”.
Writing on Twitter following the vote, she said: “So lost 92 to 94 votes hardly decisive victory and it never occurred to me that Trots Stalinists Communists and assorted hard left would gave confidence in me. I have none in them.
“I will be out tomorrow morning working hard for the people of Enfield. Just to be clear I will not be resigning. I am Labour through and through and I will continue to stand up and fight for Labour values.”
Another former minister in Mr Blair’s Government, Frank Field, resigned the party whip after losing a vote of no confidence in his constituency, blaming the anti-Semitism row and allegations of bullying among members.
Mr Blair said: “There’s lots of people associated with me who feel that the Labour Party’s lost, that the game’s over. I’m kind of hoping they’re not right.”
The former PM said the row over anti-Semitism that has engulfed the party is “ghastly” and a “matter of great sadness”.
He said he could not have imagined the row taking place in the way it did “in the Labour Party I joined, all the way through to this moment”.
“I can’t imagine that we have had three to four months debating over something where we have profoundly insulted the Jewish community in our country,” he said.
Speaking after Mr Field’s resignation, Mr Corbyn said he did not “see why he had to resign” the Labour whip.
“I invite all MPs to take part in the discussion and the debate,” he said.
“Obviously bullying and intimidation have no place whatsoever in any political party, particularly the Labour Party, but there has to be democratic debate within the party.”