Corbyn had been due to attend the unveiling of a new banner on the South Bank in central London at 9am this morning.
But just hours before, a Labour spokeswoman said he would be replaced at the presentation by election organisers Andrew Gwynne and Ian Lavery.
“Jeremy is preparing for the Clause V meeting,” the spokeswoman added, where a host of party figures will sign off on the final manifesto ahead of its official release.
Ian Lavery told press: “He [Corbyn] was meant to be here but.. he’s dealing with internal matters within the party.”
Some journalists speculated that Corbyn had dodged the poster launch to “avoid awkward questions” about the draft manifesto leak.
The Mirror’s Political Editor, Jack Blanchard, said Corbyn would “not face the media at all” this morning, “while his lieutenants are out cleaning up the mess”.
Andrew Gwynne, who did the media rounds in the aftermath of last night’s leak, was instead praised for doing an “incredibly difficult job”.
Labour’s official manifesto will be published next week, along with the Conservatives.
But the draft leaked to two newspapers was described by the Telegraph as wanting to take “Britain back to the 1970s”, while the Labour-supporting Mirror said it was the “most left-wing election manifesto in a generation”.