United Airlines has named an acting CEO after its current chief executive suffered a heart attack about a month into the job.

The company said late Monday that general counsel Brett J. Hart will take over for Oscar Munoz, who went on medical leave.

United confirmed that Munoz was hospitalized after suffering a heart attack Thursday. The company said it was too soon to know how long Munoz will need to recover.

Munoz, 56, became CEO in early September after Jeff Smisek abruptly stepped down amid a federal investigation.