Carl Icahn posts worst loss since 2008

NEW YORK -- Carl Icahn, who briefly flirted with a role as Donald Trump's Treasury Secretary, just posted his worst investment losses since the dark days of the financial crisis.

Carl Icahn
Adam Jeffery | CNBC
Carl Icahn

The 80-year-old investor's hedge fund lost 18% last year as investments in companies like Chesapeake Energy Corporation (CHK) were crushed by fears that a global economic slowdown could crimp demand for oil, copper and other commodities. That follows a loss of 7.4% in 2014, also due to declining energy prices.

"2015 was a challenging year to say the least," Keith Cozza, chief executive officer of Icahn Enterprises, said in a conference call Monday. "We are quite disappointed in our results," Cozza said.

The billionaire, known for his public battles with large companies, posted a loss of 36% in 2008 due to the mortgage meltdown. He bounced back quickly, however, with a 33% gain in 2009, a 15% rise in 2010, and a 35% gain in 2011 — a year when most hedge funds lost money.

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Since its founding in 2004, Icahn's hedge fund, which also shorts stocks, has returned 171%, or 9% annualized, the company said.

Icahn's 2015 loss follows a warning by ratings agency Standard & Poor's that it may cut Icahn Enterprises' credit rating to junk status due to its commodity sector losses.

Read MoreS&P may cut Icahn Enterprises to 'junk' status

S&P, which placed the company's unsecured debt on "CreditWatch with negative implications" in February, questioned the company's cash flow at a time when it has debts coming due, including $1.175 billion in senior unsecured notes due in January 2017.

In total, the company posted $6.3 billion in cash and cash "equivalents," including Icahn Enterprises' $3.4 billion stake in its hedge fund, which could be liquidated if needed. The company also touted cash held by businesses it owns and operates, such as Tropicana Entertainment Inc., which runs casinos in eight states.

But the holding company's cash dropped to $166 million, down from $1.12 billion at the end of 2014 — raising questions about its ability to repay debts and make new investments.

As of Monday, Icahn continued to spend money on new investment opportunities, including an offer to pay $7 a share to buy up the shares of Federal-Mogul that it does not currently own. Late last year, Icahn also agreed to fork over $1 billion to buy auto repair chain Pep Boys.

In the conference call, CEO Cozza said the Federal-Mogul purchase should cost $210 million. If approved soon, the cash would come from Icahn's investment portfolio. Otherwise it will come from money that's expected to be freed up from integrating Pep Boys with Auto Plus, another automotive maintenance company Icahn owns.

S&P said it will decide whether to lower Icahn's debt rating in 90 days. It cited Icahn's investments in Chesapeake, Cheniere, and Freeport-McMoRan for the ratings warning.

Read MoreIn a first, Cheniere to export US liquefied natural gas

Freeport, which explores for copper, oil and gas, is up 13% after losing 71% last year. Chesapeake is down 42% this year, while Cheniere has lost 5% in 2016.