While stocks surged Monday morning on what veteran trader Art Cashin attributed to "short covering," traders were still looking toward signs of trouble in China, he told CNBC.
More specifically, a rumor about a Chinese real estate developer defaulting on its debt has been circulating among traders, said Cashin, UBS' director of floor operations at the NYSE.
"We had a big default last week," Cashin said on "Squawk on the Street," referring to the bond default from a Chinese solar company that shook global markets. "Are we going to get a 'Bear Stearns' moment? Is the contagion likely to spread? Crimea continues to take the headlines. China continues to be a problem."
(Read more: Will the Crimea relief rally last?: Polcari)
Traders seemed to look past major developments on the Crimean peninsula over the weekend, where leaders held a referendum to secede from Ukraine and on Monday applied to join Russia.
The U.S. and European Union announced economic sanctions against Russia that included asset freezes and travel restrictions, but Cashin said Wall Street saw those measures as a "slap on the wrist."