Jon Lansman, the Jewish founder of pro-Corbyn campaign group Momentum, is supporting Rebecca Long Bailey's bid to replace him as Labour leader, it has been reported.
Mr Lansman has been informally advising Ms Long Bailey, who is expected to soon formally announce her bid, and is likely to join her campaign in a senior role, The Sunday Times reported.
Ms Long Bailey, the shadow business secretary and MP for Salford and Eccles, is predicted to likely pick up endorsements from the party's left.
But critics of the outgoing leader have warned against, picking a successor who continues the Corbyn project.
Corbyn critic Neil Coyle said: If the answer to the worst defeat in a century is continuity Corbyn, people haven’t understood the message the voters have given us."
On election night, Mr Lansman said Mr Corbyn had "always been a reluctant leader".
He clashed after the election result with former Labour home secretary Alan Johnson, who told him on live TV: "
"The working classes have always been a disappointment for Jon and his cult," Mr Johnson said. "I want Momentum gone. Go back to your student politics.
"Corbyn was a disaster on the doorstep... everyone knew he couldn't lead the working class out of a paper bag."