Once the U.S. and China have reached a trade deal, the world's largest economy will amplify tensions with the European Union, according to the chief economist of the Organization for Economic Co-operation and Development (OECD).
Her comments come as market participants continue to monitor the prospect of a comprehensive trade agreement between Washington and Beijing.
On Thursday, President Donald Trump said the U.S. had found common ground on some of the toughest points in trade talks, adding a deal could be agreed in the next four weeks.
Chinese President Xi Jinping reportedly echoed the optimism over a possible deal, but the White House warned some sticking points remain unresolved.
"Even once we are done with the U.S. and China, the U.S. will turn to Europe," Laurence Boone, chief economist at OECD, told CNBC's Steve Sedgwick at the Ambrosetti Workshop in Italy on Friday.
"So, I think by undermining the multi-lateral rules-based system on trade, we have just injected a massive dose of uncertainty in the world that will stay with us for a long time."