In a scathing attack, Mr Khan said Mr Corbyn had failed to win the trust of voters and that Labour was “extremely unlikely” to secure a return to power as long as he remained leader.
But a spokesman for Mr Corbyn’s campaign said Mr Khan won the mayoralty standing on a Labour platform under Mr Corbyn’s leadership and with the backing of a large number of the new members who he had inspired to join the party.
A key trade union ally of the Labour leader described Mr Khan’s intervention as “disappointing” and warned that the Labour members in the capital would feel “let down” by his actions.
A spokesman for the Jeremy for Labour campaign, said Mr Corbyn had even defended Mr Khan in the Commons at Prime Minister’s Questions when David Cameron accused him of having links with extremists.
“Sadiq Khan is entitled to his opinion,” the spokesman said.
“But he won the London mayoralty, as others have pointed out, by standing on a Labour platform under the leadership of Jeremy Corbyn backed by the huge numbers who have joined our party to support Jeremy and now campaign for Labour.”
Matt Wrack, the left wing general secretary of the Fire Brigades Union and a strong supporter of Mr Corbyn, said Mr Khan’s comments were “a little bit disappointing but possibly no great surprise”.
“Sadiq comes from that part of the Labour Party that was in government under Blair and Brown,” Mr Wrack told BBC News.
“It is disappointing nevertheless. Jeremy Corbyn gave full support for Sadiq in his campaign for mayor, as did a number of unions including my own.
“Sadiq hasn’t consulted us or Labour Party members across London about this latest statement. I think a lot of people will be quite let down by that.”