Fitch ratings agency on Friday revised the outlook on Belgium from stable to negative, criticising the country's efforts to tackle public debt.
The revision means the agency could in the medium term lower Belgium's "AA" credit rating, the third-highest level.
"Budget deficit reduction has stalled in 2014," the agency said in a statement, estimating that the general government deficit was likely to be around three percent of Gross Domestic Product (GDP) this year, 0.6 percent above the original budget target.
And "the draft 2015 budget indicates a slower path of budget deficit reduction in 2015 and 2016 than previously planned," it added.
Fitch also noted that Belgium's GDP outlook "has worsened".
"The agency projects growth of 0.9 percent in 2015 (from 1.6 percent previously) and 1.1 percent in 2016. Fiscal consolidation and a weaker outlook in the eurozone are likely to weigh on GDP growth next year," it said.
Earlier this month there were violent protests in the Belgian capital Brussels during demonstrations against the new government's plans to introduce austerity measures.