Investors should be most concerned about about the yuan when weighing the situation in China, UBS' Art Cashin and longtime bull Jeremy Siegel said Thursday.
"They've lost a good deal on foreign exchange reserves. That's going to present a little bit of a problem for them," Cashin, the bank's director of floor operations, CNBC's "Squawk on the Street."
China's foreign exchange reserves fell by $512.66 billion in 2015 to $3.33 trillion, central bank data showed on Thursday. That marks their biggest annual drop. The People's Bank of China (PBOC) had set the yuan midpoint at 6.5646 per dollar on Thursday, 0.5 percent weaker than Wednesday's fix, the biggest fall between daily fixings since the devaluation began in mid-August.
"What this does is, again, push inflation on the rest of the world at a time when central bankers are struggling to get inflation up to its target. That's one reason why I think the Fed's going to stay its hands," Siegel, the finance professor at The Wharton School, told CNBC's "Fast Money: Halftime Report" on Thursday.
Chinese equities fell 7 percent for the second time this week, triggering the newly placed circuit breakers. In fact, the Chinese trading session only lasted 29 minuted before being shut down.