Blackstone Group strategist and investment icon Byron Wien warns investors not to get too excited over the stock market hitting record highs because a big plunge looms on the horizon.

"I think this is going to be a down year for the market. … I think it's going to struggle in the second half," the vice chairman at Blackstone Advisory Partners told CNBC.

The S&P is up more than 6 percent for the year, while the Dow's nine-day winning streak as of Wednesday's close is its best run since March 2013.

But the rally has been driven by defensive sectors such as telecoms and utilities amid concerns about global instability including Britain's recent vote to leave the European Union, Reuters explained.

Wien's concerns are focused on valuation levels that appear extended over historical averages.

"I don't think we're going to have a bear market," Wien said. "I just think the market is very fully priced, and we could have a pullback from current levels," he said.

“Long-term, I'm positive about equities," he said. "But they're a little ahead of themselves now," he added.

Other experts agree that the current rally may be running on fumes.

"The recent rally has been more shallow and has been confined to a few sectors," Art Hogan, chief market strategist at Wunderlich Securities in New York, told Reuters. "Any pullback was to be expected given that the Dow rallied for nine straight days and you have to see today's action in that context. The broader macro context hasn't changed."

To be sure, U.S. economic growth stumbled sharply in the first quarter to its slowest pace in two years as consumer spending softened and a strong dollar continued to undercut exports, but a pick-up in activity is anticipated given a buoyant labor market, Reuters reported.

"The economy essentially stalled in the first quarter, but that doesn't mean it is faltering," said Newsmax Finance Insider Joel Naroff, chief economist at Naroff Economic Advisors in Holland, Pennsylvania. "Some of the restraints to growth are dissipating. Growth is likely to accelerate going forward."

Many other analysts predict the economy could accelerate in the second half of the year.

"The economy is looking better," David Kotok, the chief economist at Cumberland Advisors, told NPR. And despite weaker-than-expected jobs growth in the month of April, Kotok says, if you look over the past few months, both "wages and jobs are in a positive trend."

This year has seen pretty anemic growth so far for the U.S. economy — with gross domestic product increasing at less than 1 percent.

"I think real GDP growth will be stronger for the rest of the year," says Mark Zandi, chief economist of Moody's Analytics. "The bottom line is that the economy is performing reasonably well, and all the economic trend lines look good for the foreseeable future."

(Newsmax wire services contributed to this report).

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