A major risk to U.S. markets is looming, and it's bigger than headlines and President Donald Trump's tweets, Goldman Sachs' Sharmin Mossavar-Rahmani told CNBC on Wednesday.

The threat is the Chinese economy, the Goldman Sachs Private Wealth Management chief investment officer told "Squawk on the Street."

"We use the term that China could 'submerge' under the burden of its own debt," Mossavar-Rahmani said. "If you look at any of the debt measures in China, they're tremendously high."

Mossavar-Rahmani focused on the credit-to-GDP number from the Bank of International Settlements as a key measure of China's accumulating debt. As of the second quarter of 2016, China's ratio was 28.8 percent.

"China is about 30, the U.S. was at 12.4 percent just before the crisis. And if the U.S. didn't avoid a financial crisis with all its strength, how can we assume that China will?" the wealth manager asked.

China is still awaiting its 19th gathering of the National Congress of the Communist Party in the fall, which Mossavar-Rahmani said would weigh on the country's economic position in 2018. The meeting will determine 370 of China's Central Committee members for the next five years.

"Then we have to see, in 2018, will they put structural reforms on the front burner or does it stay on the back burner?" Mossavar-Rahmani asked.