A report for Cardiff council has warned it could find its contribution to a so-called City Deal to be "unaffordable".
The City Deal plans, announced earlier this year, require money from UK and Welsh ministers, Cardiff council and other local authorities in the area.
Cardiff council said it had to "consider all the options".
David Cameron stressed the importance of a Cardiff City deal in a BBC Wales interview last week.
But the council report said its contribution could be unaffordable in the current financial climate.
Cardiff council leader Phil Bale has campaigned for a deal, but there is a lot of negotiation to be done before it can happen.
In a statement, the authority said applying for a City Deal brought an "element of risk and cost to the council" and it had a "responsibility to consider all the options that will deliver the investment needed for a successful Cardiff and a thriving south east Wales".
A Welsh government spokesman added: "Key to the successful delivery of any future programme will be close collaboration and partnership between UK Government, Welsh Government and Local Government.
"We have had early, positive engagement with Cardiff City Council in respect of their intentions to develop a proposal for the city and region, and we will work closely with them as the proposal is developed further."
A deal to provide hundreds of millions of pounds of funding for building and transport projects in Cardiff and the surrounding areas could be in doubt.