There still may be more "dramatic" selling ahead for the stock market, top technician Ralph Acampora told CNBC on Thursday.
He's looking to see if the lows of the last week or so hold.
"If we start taking out those lows, I think you are going to start seeing some dramatic declines across the board," the director of technical research at Altaira Capital Partners said on "Closing Bell."
Acampora, known as the "godfather of technical analysis," thinks there could be another sell-off of about 10 percent.
U.S. equities dropped on Thursday, adding to October's already steep losses. The Dow Jones Industrial Average and have fallen more than 4 percent each, while the Nasdaq is down more than 7 percent this month.
Thursday's action followed Wednesday's volatile session that saw the Dow close lower and the S&P 500 and Nasdaq composite closing just below the flatline. Earlier in the week, however, the market attempted a rally. On Tuesday, the major indexes posted their best day since March.
Acampora said there is a lot of uncertainty weighing on the market, like the remarks by White House economic advisor Larry Kudlow that China has not responded positively to any of the U.S. "asks" in trade talks.
"I'm concerned about the failure to make new highs and the failure to hold the rallies. If there's one thing the market doesn't like it's failed rallies," he said.
Art Cashin, UBS director of floor operations at the New York Stock Exchange, said he believes what is happening in Italy had a great deal to do with Thursday's sell-off.
Italian bond yields jumped higher after European Central Bank President Mario Draghi said one of the risks for the economy was countries trying to circumvent EU budget rules.
"You went down, you broke the 200-day moving average in at least two key indices. You've also got the transports selling off in a manner that could cause a Dow Theory sell signal," Cashin told "Closing Bell."
The Dow Theory uses the transportation and industrial indexes to gauge the strength and weakness of market moves.
"It looked like everything could come unravelled but they didn't. There was no trap door sell-off once you broke those levels," added Cashin.
— CNBC's Fred Imbert, Miguel Pineda and Jeff Cox contributed to this report.