Centrist French presidential candidate Emmanuel Macron may be leading in the polls, but his postelection honeymoon will likely be short-lived, foreign policy expert Benn Steil told CNBC on Friday.
Macron, who wants closer European cooperation and an open economy, faces far-right rival Marine Le Pen in Sunday's election. Le Pen advocates closing the borders and quitting the euro.
The most recent polls show Macron on course to win 63 percent of the vote, with Le Pen expected to score 37 percent.
"His biggest enemy right now is apathy," the senior fellow at the Council on Foreign Relations said in an interview with "Closing Bell."
"If you look at the first round of French presidential voting, you had 50 percent of the French electorate supporting a candidate who was broadly euroskeptic."
If Macron wins, he will have to rally his new party, En Marche, for the parliamentary elections in June. While En Marche will likely emerge has the biggest party in those elections, the traditional-right center and its allies are also polling strong, Steil pointed out.
That means Macron could possibly wind up governing with a prime minister from another party, explained Steil.
"This is going to be a tough period."
And if he fails to be effective, the far right may come back even stronger in the next elections, he predicted.
However, Philippe Le Corre, a fellow at The Brookings Institution, pointed out that Macron, who has never held elected office, is a different type of candidate for France. Neither right nor left, he'll put together a grand coalition in the style of the German government, he told "Closing Bell."
"This is very new for French politics, which are very divided between left and right since World War II," he said. "We should give him a chance before saying he already failed."
— CNBC's Laura Petti and Reuters contributed to this report.