The S&P 500 will soon see a double-digit correction but investors should use it to buy not bail

 Investors should be prepared for the possibility of additional pressure in the markets, but it won't necessarily be a signal to exit, said Sam Stovall, CFRA chief investment strategist.

"We think that the S&P 500 will test its 200-day moving average, rather than just its 50-day average as it did recently, which could convert this pullback into a low-level, double-digital correction," the strategist wrote in a note on Monday.

But Stovall also said that because the Fed is likely to keep interest rates low over the next few years, this dip will be an "opportunity to buy rather than reason to bail."

The strategist said that at the end of August, the 12-month price return for the S&P 500 Growth index was 35 percentage points higher than the value index. "This month-end difference was the widest since these indices were created in mid-1970s," Stovall said. "Not surprisingly, this extreme made the market vulnerable to a selloff, which it got during the low-volume days surrounding the Labor Day Holiday."