The Federal Reserve will make its regular monetary policy announcement on Wednesday and without question, Wall Street will be watching.
To one stock market observer, though, the second-quarter gross domestic product figures also due on Wednesday is "the biggest wildcard this week" and more likely to move markets.
After all, GDP has been very tough to gauge lately.
"Coming in at -2.9 percent last quarter was a shock to everybody," David Zervos, chief market strategist at Jefferies, told CNBC on Tuesday. "I think, you know, that [the GDP number this week] could be very high or very low and really get some people sort of hot and bothered."
GDP is the total value of all goods and services produced within a country over a given time, so it's a gauge on the health of a country's economy.
Lately, GDP data have been contrary to other economic indicators that suggest growth, Zervos said on "Squawk on the Street."
Take consumer confidence, for example, which soared to its highest level in nearly seven years on Tuesday. The Conference Board's measure of consumer confidence came in at 90.9 in July, the highest reading since October 2007. Being as a pickup in consumer confidence has lagged relative to the economic recovery at large, Zervos called it "fantastic news."
"The GDP data is really telling you a very, very different story from virtually every other piece of data out there, so that's why there's this risk of surprise," he said, adding that some of the discrepancy could be blamed on the Affordable Care Act, which was enacted earlier this year.
"The medical payment side of it, some of the intricacies of the data and the ACA coming online—these have all made GDP a very complicated story," he said. "That's why I think there's potential for something to come out that's surprising to the market. It's been inconsistent. So either we're going see one story or another story develop."
Whatever the case may be, Zervos said Wall Street will also look forward to the July jobs report on Friday.
—By CNBC's Drew Sandholm.