If this happens, the S&P 500 is in real trouble: Yamada

After two tough sessions for the market, the S&P 500 hit a one-month low on Tuesday morning before turning positive for the day. But technical analyst Louise Yamada says the stock slide isn't over just yet.

"I don't think the pullback is already over," Yamada, of Louise Yamada Technical Research Advisors, said on Tuesday's episode of "Futures Now." "I think that it's an interim pullback, and we've certainly seen what we've expected, in the Internet and biotechs coming off. And I think that although they may bounce, there's probably still a little bit more to go on the downside."

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Worse yet, the selling could spread to other sectors, such as aerospace and consumer discretionary stocks.

"What we're concerned about it whether or not some of the other stocks that have gone straight up are starting to move sideways, either in a consolidation or in preparation for some distribution," Yamada said, referring to a bearish pattern that indicates a market top. "It's a little iffy here."

What would cause real concern is if the S&P trades below 1,750.

"If we break that level, that will be the first lower low that we would have seen all the way back to 2011, really," Yamada said.

Below 1,750, support lies at 1,650, which is "where the 2009 uptrend would be by midyear," she wrote to CNBC.com. That is about 11 percent below current levels.

Yamada says the weakness in stocks lines up well with broader bearish indicators, such as the fact that 2014 started with a weak January, and is a midterm election year.

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But it's not all bad.

"The one positive, of course, is that 2015, as a year ending in 5, has a very good record of being an up year," the technician said. "That's the silver lining."

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