Jeremy Corbyn "certainly could" become prime minister, Labour's former leader Ed Miliband has said.
Miliband, who has stepped back from the political front line since losing the 2015 general election, did not rule out taking a post in a Corbyn cabinet, saying he would want to "contribute in some way."
In an interview with former Labour communications chief Alastair Campbell for GQ magazine, Miliband said that his 2010-15 leadership may have "laid some of the foundations" for the radical platform offered by his successor.
But he said that, unlike him, Corbyn had been able to give voters "a sense that he had answers big enough, bold enough, honest enough, for the moment we are in."
"I give some credit to Jeremy Corbyn on this," said Miliband, currently enjoying a new wave of popularity thanks to his Reasons to be Cheerful podcast.
"People want bigger, bolder answers to the problems that exist. I felt as leader: 'My analysis is big; are the answers big enough?'"
Labour's 2015 leadership contest felt like a choice between "a more right-wing version of Ed or a more left-wing version of Ed", said Miliband.
Corbyn won because he offered "a more radical, bolder version" than rivals Andy Burnham, Yvette Cooper and Liz Kendall, he said, adding: "If Jeremy leads a radical government that changes the country, then maybe I laid some of the foundations."
Asked if Corbyn could make it to 10 Downing Street, Miliband said: "I can't guarantee that. It is not in the bag, but it certainly could happen."
Pressed over whether he would take a role in a Corbyn government, he said: "I think that is for the future. I don't know. I want to contribute in some way, but I am happy with what I am doing."
Miliband declined to say whether Corbyn should attend a state banquet for Donald Trump if the US President's mooted state visit goes ahead, saying that this was a matter for the Labour leader to decide.
But asked what he will do if Trump comes to the UK, he replied: "I am on the demo. Definitely."
Miliband's interview with Mr Campbell can be read in full in the April edition of GQ.