S&P is ‘on borrowed time’—go short: Technician

US propping up world ... for now: Pro
US props up world ... for now: Pro   

The S&P 500 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."

"I do not draw the lines. ... The lines draw themselves. It bounces perfectly, perfectly, perfectly, and guess where we're fading just now? Right off the top" of the channel, he said.

"At a minimum, I think we go to the bottom of the channel, which implies about a 5 percent drop. Short the SPY."

Read MoreA taxing problem: How traders are playing year-end selling

Options trader Mike Khouw is similarly bearish, noting that the S&P's valuation has crept higher.

"The S&P is trading about 17.7 times earnings, that's about a turn and a half richer than it has historically, about 16.2 times," Khouw said Friday.

"At the very least, you'd expect that the multiple would revert back to the mean, that's about an 8.5 percent decline from where the S&P traded today. And only off 3.5 percent from the highs, it's not a big stretch to think that we could see it fall another 8.5 percent here."

To take advantage of such a move, Khouw would advocate buying the S&P 500 ETF March quarterly 200/185 put spread for $3.80. This trade will make money if the SPY is below $196.20 at the end of March, or 2.2 percent below Monday's opening price.

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