Andrew Fisher, who was Corbyn’s policy director when he was Labour leader, said the row was “a very unedifying spectacle played out in public between the two most prominent people associated with [the party] by a mile”.
“If they can’t get their act together between them, it doesn’t give people a lot of faith that the vehicle can get off the ground,” he told BBC Radio 4’s World at One programme.
Fisher said that while there was clearly “enthusiasm” for the party from the public, the infighting may push some potential supporters towards the Green Party instead.
“I suspect a lot of people… have probably looked at this and gone, ‘Nope, not worth the bother. I might join the Greens with Zach Polanski, who is an articulate leader in a stable party that is making left-wing arguments’.” he said.
“And maybe that’s the vehicle that will take off as a result of this.”
Polanski, who was elected as the new leader of the Green Party of England and Wales earlier this month, said thousands of people had joined the party since he took over, with its membership passing 75,000 this week.
Asked whether rows within Your Party could benefit the Greens, Polanski told the BBC: “I really like Jeremy Corbyn and Zarah Sultana, and my door’s always open for conversations.”
But he added: “The Green Party just really have momentum at the moment, and we don’t have time to waste.
“I know a lot of people in this country right now want to see a party ready to challenge Reform and challenge this deeply unpopular Labour government, and that’s exactly what I intend to do.”