Questions remain over government assurances that NI will receive £18bn pledged under the St Andrews Agreement, Finance Minister Sammy Wilson has said.
Secretary of State Owen Paterson said Northern Ireland would receive the capital investment funding which was promised in 2006.
Mr Wilson said it was important to know when exactly the money would be made available between now and 2017.
"I suppose the devil is in the details," he said.
Mr Paterson has declined to say how the funding would come, saying the "nitty gritty details" are still being negotiated ahead of next week's Spending Review announcements.
Economist John Simpson told the BBC that he believed a total of £14bn will have been invested in Northern Ireland by 2014-15, the end of the period covered by the Spending Review.
He added that he believed the government was then hoping that with an improved economy it would make up the rest of its commitment over the following three years.
Mr Wilson said he wanted to clarify whether the money would be made available at the outset, dispersed evenly over the next seven years or only at the end of the period.
"Of course that's important for the construction industry and the infrastructure projects which need to be carried out," he said.
Mr Wilson said he needed to clarify how much of this figure was dependent upon raising money by selling assets or taking on borrowing commitments.
"If he's saying for example, once we get through the next four years a lot of that capital spending will be made available, that's not going to be very helpful to us.
"If it's dependent on us raising money from capital receipts and the Treasury allowing us to keep them, of course it's difficult to sell assets at present, so it wouldn't be very meaningful in the immediate period."
Deputy First Minister Martin McGuinness welcomed Mr Paterson's comments.
"Over the course of recent weeks we have built a strong political consensus and put a strong case to the British Treasury that the commitments entered into by the previous British government concerning significant investment in the north needed to be honoured," he said.
"It now appears that the British government have moved to recognise that moving away from these commitments and specifically the Investment Strategy is not acceptable.
"This shows what is possible when we pull together and put a strong united case forward."
Mr McGuinness and First Minister Peter Robinson had both raised concerns that the £18bn investment pledge promised by the Labour government could be halved, amid warnings from Mr Paterson that Gordon Brown had "written an cheque he could not cash".
However, Mr Paterson said on Thursday that the government would fulfil the commitment.
Speaking to Radio Ulster on Friday morning, Mr Paterson said Northern Ireland was an issue of real interest to Prime Minister David Cameron and Deputy Prime Minister Nick Clegg, who was in NI last week.
"I'm here to bat for Northern Ireland in the cabinet," he added.
"At a time of incredibly tight spending - when we're going to have to reduce the total spend in order to stop the UK state borrowing £270,000 a minute - it is my job to stick up for Northern Ireland."
Mr Paterson said that while the investment pledge would be honoured, something had to be done about Northern Ireland's "very, very high" dependence on public sector spending.
"For the last three years I've been saying that it is unsustainable, we need to begin to work on that," he said.
"We need to begin to revive the private sector - I've got ideas for turning the whole of Northern Ireland into an enterprise zone."