The is just 9 points off a trigger point that will see it tumble 30 percent, veteran trader and economist Steen Jakobsen told CNBC on Thursday.
The index, which tracks the U.S.'s 500 biggest companies, touched a new high on Wednesday, and closed at 1,890.90 points, up 2.3 percent on the year. It has grown steadily since mid-2011, when it touched a low of 1,011.52.
Jakobsen, the chief economist and chief investment officer at Saxo Bank, warned the index was just points away from the key 1,900 level, which could herald a 30 percent correction. This would see the S&P tumble to 1,330.
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The S&P plummeted nearly 50 percent between May and November 2008 in the wake of the financial crisis, falling to a session low of 741.02 in November. However, it has enjoyed a long bull run since then.
The economist said that the index was overdue for a correction.
"Equities are the only asset class that have not been impacted by this crisis — we had commodities and then we had fixed income. So for the crisis to play out fully, we need to go into equities. That will happen on lack of earnings, the lack of growth coming into the sector," Jakobsen told CNBC.
He said that typically equity markets corrected 10 percent once a year, and corrected 25-30 percent every five years.
"So statistically we are overdue (for a fall-off)," he said.
Jakobsen added that the stock market was currently stoked by corporate stock buybacks and investors who were only interested in buying equities and corporate debt.
He predicted the S&P would soon suffer from a decline in real corporate earnings, as well as a "very significant" global slowdown.
"I even think there is a risk Germany will hit recession by the end of this year," Jakobsen said.
Francesco Filia, the CEO and CIO of Fasanara Capital, concurred that a 30 percent correction was possible. The investor has an "avoid" rating on the U.S. equity market, preferring its Japanese and European equivalents.
"I think the S&P is deceptively unvolatile. It behaves like a bond. I do not think that is going to be sustainable," Filia told CNBC.
"I think that the 5-10 percent corrections the type of which we saw at the end of January can return to be the norm and that a bigger correction is well possible, given that valuations are so much higher than fundamentals."