Permanent stock market bull Jeremy Siegel doesn't seem so bullish about economic growth last quarter. And if growth doesn't pick up, it could derail one of the most bullish stock market calls for this year.
Siegel, a finance professor at the University of Pennsylvania's Wharton School, told CNBC on Friday that he thinks last quarter's GDP numbers could come in as low as 1 percent. That's too low to support his forecasts for the Dow surpassing 18,000 points.
In an interview with CNBC's "Squawk Box," Siegel said he needs growth to round out at 3 or 4 percent this year in order for the Dow to reach his year-end target after Thursday's deep selloff. Siegel attributed the sharp declines in major averages to a rotation into dividend-paying stocks, which look more attractive than 10-year Treasurys.
Siegel called the rotation "healthy" for stocks.
"We need to see some acceleration," Siegel said. "This first quarter, when we get this announcement later this month, it's going to be terrible. I think it might be around 1 percent. What the market is hoping for is 3.5 and 3.75 percent at least over the next three quarters. There will be disappointment if we don't get that but ... I don't think that will mean a bear market or a serious selloff."
In December, Siegel forecast growth at between 3 and 4 percent for this year.
—By CNBC's Jeff Morganteen