The weakened global economy may not yet have seen the worst of Europe's rolling debt crisis, which could take at least another two years to resolve, Roger Altman, founder and CEO of Evercore Partners, told CNBC Thursday.
As debate deepens in markets over whether Spain will accept an international rescue package, Altman said Madrid would ultimately be forced to accept the inevitable. (Read more: Will S&P Ratings Cut Finally Push Spain Into a Bailout?)
"I'm afraid that we're only around half-time in the euro zone crisis, "Altman said on CNBC's "Squawk Box," saying that the Continent's economic woes were being magnified by a "darkened" outlook for the global economy.
"Maybe the worst of the euro zone crisis from a market point of view is behind us," Evercore's chief said. "But in terms of the big picture, this is going to take another couple of years [to resolve], at least."
Altman lauded the European Central Bank's Hail Mary pass of buying up distressed euro zone debt, but added that Spain had to take the initiative and accept the bailout that the country's leaders have been reluctant to accept in public.
The ECB's pledge to intervene in secondary markets "is a very serious big pledge, and it's just up to Spain to actually apply for that and accept the reforms that are going to be necessary," Altman said. "They're going to have to do it. I don't think they have any alternative."
Given the sharply decelerating global economy, Altman also praised the efforts of the Federal Reserve .
Both central banks "are exactly in the right place in terms of maximum open throttle" on monetary policy, the banker said. He was especially complimentary of the Fed's massive bond-buying efforts to reinvigorate the U.S. economy.
"I think history is going to judge that the actions of the Federal Reserve from late 2008 to the present have been heroic, and they are going to be a textbook case of how to respond to a financial collapse," Altman added.