A pioneer in the field of chart-based trading, Acampora said the technical damage that has resulted in the Dow Jones Industrial Average DJIA, +1.06% and the S&P 500 index SPX, +1.06% erasing all of their gains for 2018, and the Nasdaq Composite Index COMP, +1.75% falling into correction territory—usually characterized as a decline of at least 10% from a recent peak—will take months to repair.

"From a technical perspective, the damage that has been done technically to the stock market is much, much worse than people are talking about," he told MarketWatch in a phone interview on Tuesday.

Acampora cited a break down of so-called FANG stocks—a quartet of technology and internet-related companies that include Facebook Inc. FB, -0.96% Amazon.com Inc. AMZN, -1.17% Netflix Inc. NFLX, -1.85% and Google-parent Alphabet Inc. GOOGL, -0.49% —as the clearest sign that the worm has turned on the bull market.