Zen, who is under investigation in Hong Kong for possible national security law breaches, was previously given permission by a court to go to Rome last month to attend the funeral of retired pope Benedict XVI, who died on December 31, aged 95.

Writing on his Facebook Tuesday night, Zen said he had been suffering from frozen shoulders and back pain before his departure to Rome and has been sick and staying at the monastery after returning to Hong Kong on January 7.

He said his situation worsened in the following days with his hands starting to swell up, and he experienced shortness of breath on the first day of the Lunar New Year (Jan 22), which saw him admitted to the hospital to get checked.

“The symptoms got me thinking about the lung illness that sent me to the hospital for three weeks in 2016…Luckily, further inspections have confirmed the infection wasn’t the same as six years ago,” he wrote.

The 91-year-old also thanked nuns and doctors who looked after him and asked people not to worry about him.