Oscar Munoz, named chief executive of United Continental Holdings just one month ago, has been hospitalized, the company said Friday.
The Wall Street Journal reported that Munoz suffered a heart attack Thursday and is being treated at a Chicago hospital.
United Continental, the parent of United Airlines, acknowledged that Munoz was hospitalized but did not explain why.
"We have been informed by Oscar's family that he was admitted to the hospital on Thursday and we will provide further details as appropriate," the company said in a brief statement.
"In the meantime, we are continuing to operate normally. Our thoughts and prayers are with his family and we are respecting their privacy."
Munoz, 56, was named CEO of United Continental on September 8 after the surprise ouster of Jeff Smisek linked to a federal investigation into allegedly inappropriate dealings with the New York regional transportation authority. Two other top executives also resigned.
The company immediately replaced Smisek with Munoz, president and chief operating officer of CSX Corporation, a US rail operator.
News of Munoz's illness sent United shares plunging 4.5 percent to $55.15 in afternoon trade on the New York Stock Exchange.