A crash-out Brexit would damage Ireland's credit rating more than most other EU nations, Moody's says in its global outlook for 2020.
The New York-based agency said Ireland's 'A2 stable' grade - in place since September 2017 - would be vulnerable if the Brexit agreement is not approved after the UK's December 12 election.
While "the likelihood of the UK and the European parliament both ratifying the revised withdrawal agreement is higher than it has been for some time", the report said a no-deal outcome remained a significant risk.
"If a no-deal Brexit were to occur, the UK would fall into recession, with unemployment rising and house prices falling," Moody's said.
"The fallout would be credit negative... for its most interconnected major trading partners," the report added, identifying those most at risk as Ireland, the Netherlands and Belgium.
"The greatest disruptions would occur in multinational supply chains, especially for manufacturers in the auto, aerospace and chemicals sectors, and for regional and local economies highly dependent on these industries," it said.
"A no-deal Brexit would also be negative for UK airports, ports and multinational insurance and reinsurance companies with operations in the UK and for structured finance transactions."
The Republic's A2 rating indicates low credit risk but it is five notches below the top grade of Aaa, held by the European Union and the Netherlands.
The UK sits three grades above Ireland on Aa2 but is at risk of a downgrade to Aa3, alongside debt-heavy Belgium.
The report cautioned that UK ratification by the EU's extended January 31 deadline still would leave "cliff risks" at the end of 2020 "if the UK and EU have not agreed on terms of their future relationship".