WASHINGTON (MarketWatch) — The global economy is suffering from even bigger woes than the decision by U.K. voters to leave the European Union, Former Federal Reserve Chairman Alan Greenspan said Friday.

”This is just the tip of the iceberg,” Greenspan said in an interview on CNBC. “The global economy is in real serious trouble.”

The rejection of British voters of the status quo in Europe was fueled by a “massive slowing” in the growth rate of real incomes that is widespread across Europe, Greenspan said. This, he said, is creating serious political problems that are not easy to resolve.

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Behind the slowdown in income is the sharp drop in worker productivity, according to Greenspan. Governments have to cut entitlements to reflect this weakness, he said.

The biggest concern is not a recession, but stagnation, the former Fed chief said.

“The euro-area…is failing,” Greenspan said.

“Greece is in real serious trouble and it is not going to continue in the euro very much longer irrespective of what is going on currently,” he said.

Asked what he would do if he was still Fed chief, Greenspan said: “I would worry.”

“This is the worst period I recall since I’ve been in public service,” he said. “There is nothing like it,” he said, including the 23% drop in the Dow Jones Industrial Average on a single day in October 1987.