Jeremy Corbyn has refused to say whether he would stand down as Labour leader if the party lost the next general election.
Earlier this week, shadow chancellor and close ally John McDonnell said he “can’t see” how Mr Corbyn could stay on in such a scenario.
But the leader told Sky News he expected to win the election, and would not answer “hypothetical” questions.
Mr Corbyn has been in the job since 2015, when he replaced Ed Miliband.
A general election is expected to take place in the autumn, with Labour currently trailing the Conservatives in the opinion polls.
Mr McDonnell told GQ magazine this week that he did not want to succeed Mr Corbyn, adding that a woman should become the next party leader.
Questioned by Sky’s Sophy Ridge, Mr Corbyn said: “We are not expecting to lose the next election. It is a hypothetical question. It is up to the members of our party to decide who the leader is.
“John gave an answer to an interview that he undertook. My answer is this: I am leading this party to go into an election. We have hundreds of thousands of members determined to win that election.”
He added: “I am determined to get a message that it is only Labour that is going to get a message out there, that it is only Labour that is going to end austerity and invest in a better future for this country. I want to lead the party to do that.”
Mr Corbyn saw off a leadership challenge from Owen Smith in 2016.
And Labour did better than expected in the snap 2017 general election but still got 56 fewer seats than the Conservatives.
Among the figures touted as potential future leaders are shadow foreign secretary Emily Thornberry and shadow business secretary Rebecca Long-Bailey.
Backbench MP Jess Phillips has also said she “might” enter any contest.
Ms Long-Bailey told BBC One’s Andrew Marr Show: “It would be fantastic for the next Labour leader to be a woman and we’ve got a whole list of amazing MPs that could vie for that position.
“But it’s a hypothetical situation at the moment. We’re fighting a general election to elect Jeremy Corbyn as our next prime minister and we think we’re in touching distance of that.”