The U.S. economy could grow sluggish as President Donald Trump moves forward with his pro-business policies, billionaire real estate investor Jeff Greene told CNBC on Monday.

“I think we have been in a period of insane ‘animals spirits,'” Greene said on “Squawk on the Street,” citing previous inaction in Washington.

The founder of the Greene Institute said that the assurances from the Trump administration that they will get things done may slow the economy, perhaps leading to a rise in interest rates.

“I think the economy is mature. … I think we’re more likely to have a slowdown to 0 percent growth than an increase to 4 percent growth, so I’m very cautious. I still maintain a lot of my core positions. But you know I have definitely cut back on my equities, by I’d say, 50 percent over the last year,” he added.

“I think there’s more room below us,” Greene said, noting that many areas of the stock market seem to be peaking.