The index needs to stay above the 1,950 level to avoid further declines, veteran trader Art Cashin told CNBC on Thursday.
U.S. stocks dropped on Thursday, reclaiming a portion of prior-day gains, as investors bypassed U.S. corporate earnings and economic reports to focus on global concerns.
Cashin, who has more than 30 years of experience on Wall Street, said the selling came as a bit of a surprise.
"By Wall Street folklore, today, the Thursday before an options expiration week, has a lot of volatility and I figured this morning we wouldn't see as much," he said on "Squawk on the Street." "But they have come in here, and they're giving back some of yesterday's gains. It would be best if the S&P stays above 1,950. They get below that—then it could get into some serious profit-taking."
—CNBC's Kate Gibson contributed to this report.