French President Francois Hollande, who last month endorsed Hillary Clinton in the U.S. presidential race, said the November ballot threatens to play out along similar lines to the U.K.'s European Union referendum.

Just as U.K. voters rejected calls from political leaders and institutions to stay in the EU, a similarly anti-establishment sentiment may be brewing in the U.S., potentially damaging relations with Europe, Hollande said.

"The arguments in the Brexit vote and in the American presidential campaign are about the same," Hollande told reporters Saturday at a NATO summit in Warsaw. "In a friendly way, may I also give some advice to the American people to make the right choice when the moment comes."