Art Cashin said the benchmark S&P 500 stock index could pull all the way back to support at 1840, a drop of about 2 percent, if it again fails to break through a tough technical resistance level.
Cashin, UBS' director of floor operations at the NYSE, told CNBC's Mary Thompson around midday, "We talked yesterday about trying to break out through 1882-85. They got very close. They couldn't break out and I think part of what you saw in the last hour yesterday was a failed-breakout fade-out. And you're seeing a little bit more of it today."
"That means the market is going to make one of two choices. They're either going to try to break out through that 1885 again, or maybe pull all the way back to support, which would be 1840."
It won't necessarily happen right away. Cashin added, "We won't know that until we see the market begin to reveal itself over the next two days."
—By CNBC's Alex Crippen. Follow him on Twitter