The 99-year-old Mahathir, who served as prime minister for more two decades, has a history of heart problems and has undergone bypass surgeries. He has been in and out of hospital in recent years, and was last hospitalised in July.
Mahathir had been due in court on Wednesday for a defamation case he had filed against the current deputy prime minister, but local media reported the hearing was postponed after his lawyer said he had been admitted to the National Heart Institute.
An aide of Mahathir told Reuters he was hospitalised on Tuesday evening for coughing due to a lower respiratory tract infection, and would be on medical leave until Oct. 25.
Mahathir served as prime minister for 22 years until 2003. He returned as premier in 2018 after leading the opposition coalition to a historic win, but his government collapsed in less than two years due to infighting.
