Art Cashin, UBS director of floor operations at the NYSE, said oil is a key factor moving the stock market.
Stocks have alternated between gains and losses in Monday's session, taking a lead from West Texas Intermediate crude oil, which dipped below $80 this morning. Since hitting a two-year low of $79.44 in early trade, oil has recovered a bit, boosting major averages.
"If oil dips back below $80, we expect to see pressure come back on equities," Cashin noted.
The stock market usually does not take its direction from oil; however, traders have increasingly viewed oil as a proxy for global growth and that has weighed on markets. Slowing growth and concerns about deflation have both sent oil down nearly 25 percent from its recent high of $107.68 in June.
Falling oil prices are a double-edged sword. The good news is they bring lower gas prices, which help consumers. The bad news is, if production is scaled back due to oversupply and declining demand, it could hurt the jobs market.
"Look at how low the unemployment is in North Dakota," Cashin said. "That's got employment there going."
Unemployment in North Dakota is the lowest of all 50 states, standing at 2.8 percent versus the national rate of 5.9 percent. Jobs on the oil fields and in restaurants and bars have been a big boon to the state's economy in the past several years.
We will get a read on the overall economy Thursday when Q3 GDP figures are released. "We're going to need a reasonably big number because we had low numbers in the first quarter," said Cashin.
Dow Jones anticipates Q3 GDP to come in at 3.1 percent after a strong Q2 of 4.6 percent growth, but a weak Q1 of 2.1 percent contraction.
"If you slip down below 3 [percent growth], there's going to be some anxiety," cautioned Cashin.
Ahead of the GDP report, the Federal Reserve will provide a policy statement Wednesday at 2 p.m. ET. Cashin said it's unlikely the Fed will make any major changes to its stance, especially because it doesn't have a press conference after the release to explain its view.
—By CNBC's Kristen Scholer.