Munoz, 57, has been on medical leave since suffering a heart attack in October.

United said last week that his previously expected first-quarter return may be delayed until the beginning of the second quarter, raising concerns about how long the second-largest U.S. airline by capacity might be without its top executive.

"I feel great, and it won't be long before we are working side by side again. Until that time, I expect to participate in key meetings and be involved in strategic planning," Munoz said in a letter addressed to employees released by the airline.

Munoz said he was headed to his Chicago home after his treatment at the Northwestern Memorial Hospital.

Brett Hart, the carrier's general counsel, has run the airline in the interim.

For months, United has aimed to allay concern that management shake-ups had left an inexperienced team of executives running its business.

In Munoz's absence, the airline has pursued the agenda he outlined in his month on the job. It struck tentative contract deals to rebuild workers' morale and improved on-time performance to boost customer satisfaction, lowest among rivals in J.D. Power's 2015 ranking.

(Reporting by Jeffrey Dastin in New York and Radhika Rukmangadhan in Bengaluru; Editing by Sriraj Kalluvila)