"South Africa, together with Turkey, are at the bottom of the ladder when it comes to policy credibility," Lutfey Siddiqi, visiting professor-in-practice at the London School of Economics (LSE), told CNBC's "Squawk Box Europe" on Wednesday.
"Credibility will be built based on action, not just on rhetoric," he added.
On Tuesday, the International Monetary Fund (IMF) cut its global economic growth forecasts for 2018 and 2019 by 0.2 percentage points to 3.7 percent. It also lowered projections for the increase in goods and services trade worldwide.
The Washington D.C.-based institute also warned the U.S.-China trade war was already showing signs of negatively impacting global growth, while emerging markets were struggling with tighter liquidity and capital outflows.
The IMF also said the balance of the risks were now tilted towards the downside, with rising interest rates likely to hurt emerging markets further at a time when U.S.-led demand growth would soon start to slow as some tax cuts expire.
To be sure, the normalizing of U.S. interest rates could pressure some emerging markets with capital outflows — most notably Turkey, South Africa, Argentina, Brazil, Mexico and Indonesia.