Art Cashin said the stock market is "oversold" after last week's downturns but still vulnerable to more selling if some technical levels are breached.

Cashin, UBS' director of floor operations at the NYSE, told CNBC's Bob Pisani around midday that "if we dip again and we get down to 4087 (on the Nasdaq) and they don't hold, we could accelerate on the sell side."

At midafternoon, the Nasdaq was down 1.7 percent to 4058. In the final hour of trading it rebounded to touch 4100 before closing at almost 4080, a drop of 1.2 percent.