Former DUP Finance Minister Sammy Wilson has advised Conor Murphy - who currently holds Stormont's purse strings - to stop complaining that the Government's financial package to the new Executive falls short of what was expected.
"All the parties drew up this enormous wish-list without securing the money to deliver it," Mr Wilson told the Belfast Telegraph on Tuesday night.
"Conor Murphy is facing an uphill job but there's no point in him moaning about it.
"The parties don't have any leverage any more.
"The Secretary of State knows that they aren't going to walk out of the Executive."
Mr Wilson said that the new Sinn Fein Finance Minister must be honest.
"He should just admit that the Executive is on a tight budget. There is no point in gurning every day about how the government did the dirt on us," he said.
"He needs to ask each of the parties to identify their big priority.
"If he doesn't do that, there will be tit-for-tat opposition around the Executive table to every spending decision he makes. They will be at loggerheads forever."
The DUP MP said that the Barnett consequentials - the formula for distributing money to the devolved regions - may have made it initially appear that New Decade, New Approach meant much more money than it did.
"The parties now need to make the best of it," Mr Wilson said.
"In 2007, the DUP went back into the Executive with Sinn Fein (after the St Andrews Agreement) in what wasn't a hugely popular move. One of our conditions was that there should be a massive financial package.
"That money didn't last long as it was hit by the recession.
"Government cutbacks wiped it out."
Mr Wilson said that "complaining about the financial package" was the wrong approach.
"There is room to cap waste by departments. Conor Murphy has good officials in the Finance Department.
"I found that if you go to the government with a genuine case, you can get money," the East Antrim MP said.
"It could be argued, for example, that Northern Ireland should get something in return for the third Heathrow runway.
"A business case can also be made to the Treasury that to enable long-term savings, a bit more money needs to be spent now to reform public services."
Meanwhile another former DUP Finance Minister, Simon Hamilton - who is now chief executive of the Belfast Chamber of Trade and Commerce - said it was vital that the return of devolution was supported by a generous financial package from the government.
He said: "We are all well aware of the scale of challenge that the new Executive faces.
"Belfast Chamber believes that it is important that the return of devolution is underpinned by a financial package that permits the delivery of important infrastructure and enables essential reform of our public services."
Mr Hamilton continued: "In Belfast Chamber's Belfast Manifesto we set our '7 Priorities for a Better Belfast'.
"This included the need to upgrade the city's water and sewerage system and the construction of the York Street Interchange.
"The inclusion of these and other vital projects in the deal that restored devolution is welcome and Belfast Chamber hopes that the funds will now be made available to realise them as soon as possible so that we can create more jobs, attract more investment and grow our economy".