Corporate revenue represents a crucial metric as investors look ahead to second-quarter earnings reports.

"The issue almost all the time is going to be, what about revenue growth?" Brian Gendreau, market strategist with the Financial Network, told CNBC.

Sales were disappointing in the first quarter, and S&P Capital IQ estimates that for the second quarter, companies in the Standard & Poor's 500 Index will book an overall revenue increase of only 0.5 percent.

Editor’s Note: Put the World’s Top Financial Minds to Work for You

"If we get any kind of disappointment in terms of revenue and earnings growth, it will be problematic," John Stoltzfus, chief market strategist at Oppenheimer, told CNBC.

"The consensus estimates have been brought down enough to realistic expectations that we'll probably not have a bad earnings season, but we'll probably see modest growth like the first quarter."

S&P Capital IQ predicts a 2.8 percent increase in second-quarter profit for S&P 500 companies.

Earnings gained 5.2 percent in the first quarter.

Revenue and profit results are more important for stocks this quarter because the Federal Reserve is talking about tapering the quantitative easing that has given the market such strong support.

Citigroup's chief U.S. equity strategist, Tobias Levkovich, says the outlook for earnings is worrisome.

"We have been a tad shocked by the surge in [the ratio of] negative-to-positive pre-announcements … that make 2009’s surge appear less worrisome in retrospect," he wrote in a commentary obtained by Business Insider.

The earnings season will begin in earnest July 8, when Alcoa releases its results.

Editor’s Note: Put the World’s Top Financial Minds to Work for You