The prime minister has refused to confirm the Welsh Government will control a new fund to replace EU economic aid for Wales after Brexit.
Theresa May told BBC Wales "across the whole of the UK" the Shared Prosperity Fund needed the "right structure and the right processes".
She said this was to ensure money is spent "as effectively as possible".
First Minister Carwyn Jones has warned replacing EU aid with a Westminster-run system would betray devolution.
As one of the poorer parts of the European Union, Wales will have received more than £5bn in so-called structural funds by 2020.
The funding from Brussels has paid for infrastructure projects across Wales, including the Ponty Lido, Swansea University's Bay Campus, the Heads of the Valleys road, Harbour Way link road and the National Sailing Academy at Pwllheli.
The Conservatives have said the new Shared Prosperity Fund is intended to reduce inequalities across the four UK nations.
Mrs May was speaking to BBC Wales' political editor Felicity Evans, ahead of the Conservative conference opening in Birmingham later.
Asked if that would be as generous to Wales as the EU has been, Mrs May said: "The point of the shared prosperity fund is that we will be looking at issues of disparities between the nations of the UK - disparities within nations and regions and deciding expenditure of money so that we are ensuring that money is being spent as effectively as possible to deliver for people."
She added that there is a "lot of discussions" taking place over how that fund "will be structured" in the future.
Asked whether the Welsh Government will have control of how that money will be spent in Wales, she told the Sunday Politics Wales programme: "I fully recognise the role that the Welsh Government has played and the role that the Welsh Government has played in decisions for Wales.
"But obviously as we look at the shared prosperity fund across the whole of the UK we want to ensure that we get the right structure and the right processes involved in that so that the money that is being spent is being spent as effectively as possible because it's about delivering for people on the ground."
On Brexit itself, Mrs May said it was right that her government was preparing for "every eventuality" but she was "confident" of getting a "good deal" with the EU.
She insisted she will not compromise on her so called Chequers plan.
"While we work for that it is right that we prepare for every eventuality that's why the government is putting preparation in for no deal as they are putting preparation in for a deal," she added.
"And it's why we have been obviously ensuring that businesses and others are aware of what might be necessary for them. But we're working to get a good deal."
The UK is due to leave the EU on 29 March 2019.