United Continental chief in hospital after heart attack
Oscar Munoz, chief executive of United Continental Airlines, suffered a heart attack on Thursday.
He is being treated at a hospital in Chicago, the company said.
Mr Munoz took over at United Continental only last month after Jeff Smisek was forced out for allegedly making deals with public officials in New York and New Jersey.
Shares fell 3.3% to $55.83 following the announcement.
The airline said it was continuing to operate normally. "Our thoughts and prayers are with his family and we are respecting their privacy," a spokesman said.
Mr Munoz is the former head Continental Airlines, which merged with United in 2010.
The company's board was waiting to hear from doctors and from Mr Munoz's family about the severity of the heart attack before deciding if an interim chief executive was needed, the Wall Street Journal reported.
It quoted a source who said the heart attack could have been mild and that he could return to work in two weeks.
United Continental has been embroiled in a scandal with the New York/New Jersey Port Authority. It has been accused of maintaining unprofitable flights that were popular with politicians in return for favourable government subsidies and better airport transit deals.
Mr Munoz was appointed chief executive in a bid to clean up the company and deal with a litany of staff and customer complaints.
The company had also struggled under Mr Smisek to merge the operations of the former United and Continental airlines.