"My father has been ill for the last 12 years but this year his condition has deteriorated significantly and in the last one month he was released from hospital for just one day before being admitted again," Arif told PTI.
Hassan has multiple lung, chest and urinary tract ailments which were being treated by specialists.
"He is admitted in the ICU of Aga Khan hospital for last one week but he is not on a ventilator," he added.
Hassan, 84, was born into a family of traditional musicians at Luna village, Rajasthan, in 1927 before his family migrated to Pakistan after 1947.
Hassan, who has a huge following in the subcontinent, cut back on his performances in the late 80s due to illness
Considered one of the most successful ghazal singers of Pakistan, Mehdi Hasasn was trained in classical music by his father Ustad Azeem Khan and his uncle Ustad Ismail Khan who were both well respected classical musicians.
Hassan tried different styles of music and there was a time in Pakistan's film industry known as Lollywood when a production was considered incomplete without his voice.
Due to his remarkable commercial and artistic success he was titled ShahenShah-e-Ghazal (The King of Ghazal singing).
He also played the role of a cultural ambassador and visited India several times.
"My father stopped singing after that visit as his health fell away and he developed lot of complications because of his age. Doctors are doing their best and we can only appeal to everyone to pray for his health," Arif said.