Labour elections and campaign coordinator Ian Lavery told a rally in Glasgow that “whatever happens” the “Corbyn project” is only beginning.
Mr Corbyn has come under pressure to say whether he will stand down as Labour leader if the party is defeated in the June 8 election.
Earlier this month, he was forced to clarify comments to BuzzFeed News in which he suggested he would look to carry on in the role even if Labour loses the election, later claiming he was speaking only about a victory for his party.
But Mr Lavery’s comments will worry Mr Corbyn’s internal critics, who are likely to call for the leader’s head if he does not win power.
Before the Labour leader spoke in Scotland, Mr Lavery said the party was in the “long, long, long process of changing politics here in Britain”.
He added: “Whatever happens in the election isn’t the end in the Corbyn project, it’s only the beginning in the Corbyn project.”