"Global growth is expanding at a healthy rate, but we are seeing a slowing momentum", the IMF's head of research Gita Gopinath said, adding there were "many important downside risks to the global economy".
The IMF, however, maintained its USA growth projections of 2.5 percent this year and 1.8 percent next year, pointing to continued strength in domestic demand.
The report came hours after data showing China's economy cooled in the fourth quarter on faltering domestic demand and bruising US tariffs, dragging 2018 growth to the lowest in almost three decades.
Ms Gopinath said a no deal could shrink the UK's economy by up to 8 per cent, a hammer blow to one of the world's biggest economies.
That's right Mark... The IMF predicts the global economy to grow at 3.5 percent in 2019 and 3.6 percent in 2020.
The IMF's latest report cited the unresolved trade war between the United States and China, and the possibility of Britain exiting the European Union without a deal.
The global growth forecast for 2020 is 3.6 percent, 0.1 percentage point lower than previously forecast.
Phil Mickelson shoots 12-under 60 at La Quinta in 2019 debut
Prior to the round Mickelson had said on Twitter he was excited to start the season but was "a bit rusty". Mickelson left a birdie putt at the par-4 17th just short before sinking a birdie at No. 18 for the 60.
The latest global economic forecasts was even more pessimistic than those released just three months ago, the International Monetary Fund emphasized that risks dominate the outlook.
However, the world´s two largest economies, now the source of most of the risk to global growth, did not see further downward revisions.
"After two years of solid expansion, the world economy is growing more slowly than expected and risks are rising", said IMF Managing Director Christine Lagarde as she presented the new forecasts at the World Economic Forum in Davos, Switzerland.
Washington and Beijing declared a 90-day truce on December 1, but the risk remains that tensions will flare up again in the Spring and "casts a shadow over global economic prospects".
According to the report, the main shared policy priority is for countries to resolve cooperatively and quickly their trade disagreements and the resulting policy uncertainty, rather than raising harmful barriers further and destabilising an already slowing global economy.
'We have done our estimates of what it would, how costly it would be to the British economy to have a no-deal Brexit, which would be a reversal to WTO rules, and that would be a decline in long-run output of about, or long-run GDP, of between five to eight percentage points'.
The figures from the National Bureau of Statistics drags full-year growth down to 6.6 percent, the slowest annual pace since 1990. "A more serious tightening of financial conditions is particularly costly given the high levels of private and public sector debt in countries".