The downgrade reflects a confluence of factors, including the introduction of import tariffs between the United States and China, weaker performances by eurozone countries, Britain and Japan, and rising interest rates that are pressuring some emerging markets with capital outflows, notably Argentina, Brazil, Turkey, South Africa, Indonesia and Mexico.
China's growth is still expected to be more than 6% next year, but the IMF's chief economist Maurice Obstfeld warned Beijing to concentrate on quality and sustainability of growth, not quantity of growth.
IMF's forecast for Singapore's economic outlook remains steady at 2.9% for 2018, but has been revised downward by 0.2 percentage points to 2.5% for the following year.
The Outlook said the global economy is expected to grow at 3.7 percent this year and next year - down 0.2 percentage points from an earlier forecast, as the trade war started to hit economic activity worldwide.
This acceleration, the world body said, reflected a rebound from transitory shocks (the currency exchange initiative and implementation of the national Goods and Services Tax), with strengthening investment and robust private consumption.
The worldwide organisation warned a full-blown trade war between the U.S. and China could have wider implications for the financial growth around the world.
The cut its 2019 U.S. growth forecast to 2.5 percent from 2.7 percent previously, while it reduced China's 2019 growth forecast to 6.2 percent from 6.4 percent.
The May federal budget forecast 3 per cent GDP in 2018-19 and the same the following financial year.
He stated, "Nigeria's growth, 1.9 per cent this year; 2.3 next year".
A decade since the economic crisis, while there has been an undeniable progress towards a safer global financial system, clouds appear on the horizon, the International Monetary Fund said in its latest fiscal stability report.
The Federal Reserve, the US central bank, has raised short-term USA rates three times this year as the American economy gains strength more than nine years after the end of the Great Recession.
"However, further reforms are needed to increase policy certainty, improve the efficiency of state-owned enterprises, enhance flexibility in the labour market, improve basic education, and align training with business needs", it stated.
"These efforts should be supported by further reductions in subsidies and enhanced compliance with the Goods and Services Tax", the International Monetary Fund report said.
The IMF announced it had reduced its outlook on the global economy to a 3.7% growth rate for this year and next, down 0.2% from what it had originally predicted in July.
Most of the "meagre gains" from growth have gone to the well-off, fuelling support for protectionism and anti-establishment leaders, said Mr Obstfeld.
Steps by the Chinese to ease some regulations could boost the economy in the near-term, but "may entail greater risks to financial stability over the medium term", the report said.