The designate head of Immanuel College, Joanna Ebner, said this week that she was "regrettably unable" to take up the post for health reasons.
In a letter in this week's JC, Ms Ebner, who had been due to arrive in September, explained, " It is my very recent diagnosis of cancer which has prevented me from serving in this prestigious role within Anglo Jewry - one to which I was very much looking forward."
She wished Immanuel "continued success as it goes from strength to strength" said she was "sorry not to be there to lead it into its next stage".
She is currently headteacher of Thomas's Kensington, a preparatory school in London.