Veteran market insider Art Cashin remains concerned about two potential surprises next year.
Cashin, UBS' director of floor operations at the New York Stock Exchange, worries about the relationship between the bond markets and the Federal Reserve, especially as the central bank continues to scale down its economic stimulus program, he told CNBC on Tuesday.
"They're expecting that they're going to be able to work out of this thing slowly, quietly and effectively," Cashin said on "Squawk on the Street." "And the bond market is giving some signs that they're not quite so sure about that. ... I would be concerned about if the bond market began to step out on its own and began to raise rates a little faster and a little faster than the Fed would prefer."
(Read more: Cashin: Expect a 3-5 percent correction next month)