Since several experts expressed their worries about the absence United Airlines CEO Oscar Munoz, the company made an announcement on Monday about appointing its general counsel as an acting CEO. The appointment came amid Munoz's medical leave after suffering from heart attack last week.

While there is no timetable for Munoz's return, United Airlines appointed 46-year-old Brett J. Hart as the company's acting CEO. According to United Airline's parent company United Continental Holdings, Hart is the company's vice president and general counsel, who has been responsible for government and regulatory affairs, corporate real estate, customer experience, corporate security, community affairs, contact center and food services.

In Munoz's absence, Hart will work closely to non-executive chairman of the board, Henry L. Meyer III and the airline's executive team to run the company, Chicago Tribune revealed.

"Brett has taken on increasing responsibility beyond general counsel over the last few years in the operations and customer facing areas of the company," Meyer III said in a statement. "I am confident in his ability to continue to implement the company's strategy and Oscar's mission of bringing United's people together around the shared purpose of becoming the best airline for our customers and employees."

Since early September, the announcement is already the second CEO shake-up at United Airlines. And under Hart's leadership, he promised to continue Munoz's agenda, which has been aimed at rebuilding the company's morale after years of strained labor relations. But with the sudden change in the company's leadership structure, a company's spokeswoman said in a statement that its board "remains actively engaged in preparing for all potential outcomes."

On Thursday, Hart will make his first presentation to investors as acting chief when the company reports third-quarter results, Reuters noted.

Despite being at an impasse on whether to appoint an interim CEO or start seeking a new one last week, United Airlines board of directors have finally decided to appoint an acting CEO to handle Munoz's responsibilities during his absence.

"The company anticipates it will today conclude the corporate governance process necessitated by the hospitalization of President and CEO, Oscar Munoz," Meyer III said in a statement Monday, as per Bloomberg Business. "The company expects to release more details either later today or tomorrow. In the meantime, the United family's thoughts and well-wishes are with Oscar."

Meanwhile, before joining United Airlines, the second largest American airline, in 2010, Hart served as executive vice president, general counsel and corporate secretary at Sara Lee. He was also a partner at Sonnenschein Nath & Rosenthal as well as a special assistant to the general counsel at the U.S. Department of Treasury.