Saudi authorities are already planning spending cuts as the world's biggest oil exporter seeks to cut its budget deficit created by the drop in crude prices.
Saudi officials have repeatedly said that the kingdom's economy is strong enough to weather the plunge in crude prices as it did in similar crises, when its finances were under more strain.
But the IMF said measures being considered by oil exporters "are likely to be inadequate to achieve the needed medium-term fiscal consolidation. Under current policies, countries would run out of buffers in less than five years because of large fiscal deficits."
The fall of the price of oil, which accounts for about 80% of Saudi Arabia's economy, has been absorbed by the hundreds of billions of dollars the kingdom has accumulated in the past decade.
Saudi's debt as a percentage of gross domestic product fell to less than 2% in 2014, the lowest in the world, Bloomberg reported. In August, net foreign assets fell to the lowest level in more than two years.
The drop in oil prices has prompted the government to sell bonds for the first time since 2007, with the kingdom's finances further strained by its war in Yemen.
The IMF expects Saudi's budget deficit to rise to more than 20% of GDP this year after King Salman announced one-time bonuses for public-sector workers following his accession to the throne in January.
A number of such one-off spending proposals this year have added to the spending needs, Masood Ahmed, director of the Middle East and Central Asia department at the IMF, told Bloomberg in an interview in Dubai.
"The budget deficit in Saudi Arabia does go down substantially as a share of GDP over the next five years but it still remains high over this period, all the more reason to identify ways in which it can be brought down further to more a manageable level," he said.
David Butter, associate fellow at Chatham House in London, told Bloomberg that a crisis is not imminent, but if the government fails to develop sustainable non-oil revenue over the next five to 10 years, "then of course, they're in big trouble," he said.
