The is just coming off of its worst week since May 2012. But according to well-known technical analyst Carter Worth of Sterne Agee, it's about to get a lot worse for U.S. stocks. Over the course of 2014, the S&P 500 has far outperformed equities around the globe. U.S. stocks are up 8.5 percent this year even after last week's selloff, while equities around the world (including the U.S.) are flat on the year, and many global markets have fallen sharply.

For Worth, this is a condition that cannot hold. "The issue of decoupling is now coming up—can we decouple from the rest of the world? ... [But] we never decouple," he said Friday on CNBC's "Options Action." "The presumption is, the U.S. is on borrowed time, and it will go the way of the rest of the world." So just how far could U.S. stocks fall? Furnishing a chart of the SPDR ETF tracking the S&P 500 (ticker symbol: SPY) Worth spots a "well-defined channel."