Watch Cashin: More selling likely if this happens

Cashin says: Watch Nasdaq low

Art Cashin said investors need to watch a key technical support level on the Nasdaq Composite.

Cashin, UBS' director of floor operations at the NYSE, told CNBC's Bob Pisani around midday, "The low this morning in Nasdaq was 4098-99. We've retested it already. On any further weakness watch that level. If you break it you'll probably get follow-on selling."

With three hours until the end of the trading day, the Nasdaq was trading at 4101.

As for disappointing earnings or outlooks from a number of retailers, including TJX Companies, Dick's Sporting Goods, Cato, and Urban Outfitters, Cashin said, "You've got to remember, the American consumer isn't King Midas. There's a limit to his resources and that's what I think you're seeing in the retailers right now."

—By CNBC's Alex Crippen. Follow him on Twitter @alexcrippen.