Have investors given up on buying the dip?

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Pisani: Indeterminate market open

Volume yesterday was slightly on the heavy side, but it's not the selling I'm concerned with, it's the buying. Or the lack of it.

Is "buy the dip" dead?

With the exception of one or two days, there has been precious little buying interest since the three-day drop in the markets from Aug. 21 to 25.

And why should there be? The markets already have had to deal with the uncertainty of not knowing when, if ever, the Fed is going to raise interest rates.

What bulls need now is some evidence that "buy the dip" does not turn into "sell any rally." Two things are necessary to avoid that.

1) Some evidence the global economy is not falling apart, starting with better data on China, which we did not get overnight. China's Flash Manufacturing PMI came in at 47.0, below expectations of 47.5, its seventh straight month of contraction (below 50) and the lowest print since March 2009.

Read More China flash PMI falls to a 6-1/2-year low in September

Every component was weaker, including new orders and employment.

That's not helpful.