Billionaire Sam Zell told CNBC he believes a correction in the stock market could be on the horizon.
"The stock market is at an all-time, but economic activity is not at an all-time," the chairman of Equity Group Investments said in a "Squawk Box" interview. "People have no place else to put their money, and the stock market is getting more than its share. It's very likely that something has to give here."
Zell also expressed concern about tensions in many parts of the world, including the threats posed by the Islamic State militant group and the Ukraine-Russia standoff.
"I don't remember any time in my career where there have been as many wildcards floating out there that have the potential to be very significant and alter people's thinking," he said. "If there's a change in confidence or some international event that changes the dynamics, people could in effect take a different position with reference to the market."
With those concerns as a backdrop, Zell said he's being very cautious about adding to stock positions and trimming where it makes sense.
"It's almost every company that's missed has missed on the revenue side, which is a reflection that there's a demand issue," he said. "When you got a demand issue it's hard to imagine the stock market at an all-time high."
He also lamented about how difficult it is to call a market top. "If you're wrong on when, that's a problem." His answer: "You got to tiptoe ... and find the right balance."
"This is the first time I ever remember where having cash isn't such a terrible thing, despite the fact that interest rates are as low as they are," he added.
