Apple stock on Wednesday posted its biggest drop since 2008, and it still has plenty of room to tumble further, says Paul Schatz, president of Heritage Capital.

Indeed, when all is said and done, several years from now, the shares could be standing 50 percent to 70 percent below their Sept. 21 peak of $705, he tells Yahoo.

A 70 percent plunge would produce a price of $211. Apple declined 6.4 percent, the biggest drop since Dec. 17, 2008, to $538.79 at the close Wednesday in New York, erasing $34.9 billion in market value. The stock has advanced 33 percent so far this year.

Editor's Note: This Wasn’t an Accident — Experts Testify on Financial Meltdown

On a fundamental basis, investors are overestimating Apple’s growth, Schatz says.

As for the technicals, Apple may have room to rise further in the short term, he says. "But what we saw in that 20-plus percent decline [to $505 intraday in mid-November from $705] was just the first leg down of a multi-year decline.”

Any upward move is a selling opportunity, Schatz says. "If your thesis, like mine, is that long term, Apple is going to be sub-$500 or sub-$400, then you can't get too greedy on the upside, because the upside is going to be fleeting."

Dennis Gartman, publisher of The Gartman Letter, also is bearish on Apple.

“If somebody put that [Apple stock-price] chart in front of you and didn't tell you what it was, you wouldn't be buying it,” he tells CNBC. “You'd look at that and say that rally is something to be sold."

Editor's Note: This Wasn’t an Accident — Experts Testify on Financial Meltdown