It may be too soon for investors to reallocate away from U.S. stocks into emerging markets, according to Mohamed El-Erian.

El-Erian, the chief economic adviser to Allianz SE, says that the macroeconomic backdrop isn’t favorable for developing nations even as a growing chorus of fund managers and strategists from UBS to Morgan Stanley Wealth Management tout their potential.

The S&P 500 Index outperformed the iShares MSCI Emerging Markets ETF by 20 percentage points in the first three quarters of 2018, leading some to believe the trend was due to reverse.

“Investors need to be cautious,” El-Erian, who is also a Bloomberg Opinion contributor, said on Twitter.

“History suggests that rising oil prices, strong dollar, tighter global liquidity conditions and slowing global growth can be a disruptive combination for quite a few emerging economies.”

To his point: Crude oil has climbed toward a four-year high, while the greenback has been strengthening since April. Federal Reserve Chairman Jerome Powell signaled last week his desire for gradual interest-rate hikes next year, and International Monetary Fund Managing Director Christine Lagarde said the global growth outlook is dimming amid the U.S.-China trade war.

Anastasia Levashova, a fund manager at Blackfriars Asset Management in London, is also skeptical about a big emerging-market rally. She cites the trajectory of U.S. interest rates, the dollar and political tensions from Europe to the Middle East, Africa and Brazil.

“I’m on the cautious side,” she said. “It seems the upside is limited.”