A more severe downturn in emerging markets, not domestic inflation, is the "biggest risk" to the U.S. economy, a top economic advisor to President Donald Trump told CNBC on Wednesday.

"I'm very concerned about emerging markets. If you look at the indices, they're heading in a way that's a little bit troubling," said Kevin Hassett, chairman of the Council of Economic Advisers.

He said he's watching Turkey, Venezuela, Argentina and China to see if stresses "lead emerging markets to head into a direction that's more extremely south than we've seen so far."

"That could come back and haunt the U.S. a little bit," he warned in a "Squawk Box" interview. He said council economic models concur with the International Monetary Fund's decision to trim its global growth forecast to 3.7 percent for this year and next.

Another trouble spot for global growth is rising oil prices, he said.

The IMF on Tuesday cut its growth forecasts for the U.S. and China to 2.9 percent and 6.6 percent, respectively, this year, and 2.5 percent and 6.2 percent, respectively, in 2019.

Hassett countered by saying, "We're looking at [U.S.] GDP growth of about 3.5 percent for this year, and carrying on to something north of 3 [percent] next year. That's a little more optimistic than they are."

He did not offer an outlook on China's economy, but he said the White House is hopeful the two sides can resolve their differences on trade. "But make no mistake, President Trump is serious about it. If they don't behave a little bit better, stopping stealing our intellectual property and lower their tariffs on our products, then this could continue longer."

Hassett also told CNBC he would let the president's comments expressing displeasure with the Fed hiking interest rates stand on their own. But he did make a case, like Trump did Tuesday, that budding signs of inflation are not posing a risk to the economy.

"We at the White House really do respect the independence of the Fed," Hassett said. "The fact is, the president's respect for the independence is clear in the quality of people we sent over there."

Before joining the Trump administration, Hassett was an economist at the American Enterprise Institute. He was also formerly a senior economist at the Federal Reserve. He's also been a consultant to the Treasury and an advisor on Republican presidential campaigns, including Mitt Romney's unsuccessful White House run in 2012.