The Assembly remains committed to improving the A5 despite the Republic pulling out of a funding deal, according to Finance Minister Sammy Wilson.
The Irish government had agreed to contribute £400m towards upgrading the Londonderry to Aughnacloy road but Taoiseach Enda Kenny reneged on the deal last week.
He said on Friday the Republic could only afford to provide £42m.
Mr Wilson said even that money was still a long way off.
The decision has been seen as a betrayal and hammer blow to the economy of the north west.
Local politicians said they were devastated by the Irish government’s u-turn on the promise.
Mr Wilson said there was no guarantee that the £400m set aside by the Assembly for the road would not be spent on other projects in the region.
The Finance Minister said: “We have had a promise of £40m, we had a promise of £400m as well, so I think we've got to bear in mind that it was being reneged on in the past. It might be reneged on in the present, until the money is actually there we can't be certain what's going to happen.
“All we can say is the executive made the commitment on Thursday after the executive meeting that we believe that there needs to be an improvement in the roads infrastructure in the west of the province.
“When the money becomes available then it will be done.”
Mr Wilson said the money from the Irish government would not be “on the table” until 2016/17 at the earliest.
Speaking on TV yesterday he said: “The executive has given a commitment that when the money becomes available we will do those parts of the road we can afford to do.
“We will prioritise those parts |of the road which most need |redone but we know that the money is not going to become available from the south until 2016/17.
“It is an international project and it must be joint funded.”
The total cost of the 55-mile upgrade — which would create a key corridor route linking Dublin to the north west — was to be £850m.
Mr Wilson said because the executive budget only ran until 2014-15 its contribution to the A5 would now be spent elsewhere.
“I think after the initial furore there has been about the way some people feel there's been a betrayal on this obligation by the government in the Republic, we will get down to the business of looking at how we can spend the money,” he said.
Earlier this week, the Irish government said it remained “politically committed to the A5”.