"I am still concerned that one day you'll see a break like you had a few weeks ago," Icahn said at the Reuters Investment Outlook Summit in New York on Monday, "but it won't come back."

With the Standard & Poor's 500 index now up more than 10 percent for the year and trading at 2,041, many investors have put October's short-lived slide behind them, saying low interest rates and a growing mergers and acquisitions boom will continue to fuel the bull market.

But Icahn is more concerned and is predicting a downturn. "It's really a question of when that is going to happen, in my opinion. It could be three years, it could be three months, it could be three days. But I really do believe there will be a major correction in the next three to five years, at least."

Even as many investors see blue skies ahead, Icahn is taking precautions. "We short S&Ps against a very large portfolio. We have the benefit of not having to worry that much about hedge fund partners."

Icahn, who at age 78 has lived through his fair share of ups and downs, is more cautious, however, saying that oil companies, which have benefited from easy money but are suffering now amid a supply glut, could be experiencing a real bubble.

Acknowledging that his more worried view is not the norm on Wall Street these days, Icahn said "I like being a minority. I am not saying go short the market, I'm talking in general terms."