Yavneh College's plans to open a primary section in September have received a setback after Hertfordshire Council said that it could not provide funding this year.
The proposed two-form entry school has been seen as vital to meet the demand for Jewish primary school places in outer north-west London.
But the council said it was unable to afford a £4 million grant for a new primary building on the site.
Sue Nyman, chairman of Yavneh's governors, said: "We are extremely disappointed. If you are a parent in Borehamwood with a child going into reception in 2012, it's a huge blow."
But she stressed: "This is not the end of the story. We have been told the application will be reconsidered next year."
In the meantime, the school would continue to liaise with the council to secure funding for 2013, she said. But it would also pursue the possibility of pursuing private donations with the hope of still being able to open the primary section next autumn.
"Miracles happen - especially at this time of year," said Mrs Nyman.
Hertfordshire councillor Morris Bright said that the situation was "frustrating. Local councillors, the school and many residents can see such a school is much needed."