The health condition of India's former president Pranab Mukherjee, who underwent a brain surgery last week, deteriorated further on Wednesday due to lung infection, the hospital said in a statement.

Mukherjee, 84, has been on a ventilator ever since his major surgery for a large brain clot.

He is being treated at Indian Army's Research and Referral Hospital in New Delhi.

"There has been a decline in the medical condition of Pranab Mukherjee as he has developed features of lung infection. He continues to be on ventilatory support and is currently being managed by a team of specialists," said the hospital.

Mukherjee, who served as India's president between 2012 to 2017, had also tested positive for COVID-19 prior to his brain surgery.