Former President Pranab Mukherjee on Monday underwent a brain surgery at the Army's Research and Referral (R&R) hospital for removal of a clot, sources said.
Mukherjee, who was unwell, was hospitalised on the advice of the doctors and had tested positive for COVID-19 prior to the surgery.
"Former President Pranab Mukherjee underwent a successful brain surgery for removal of a clot at the Army's R&R hospital," sources told PTI.
"He is critical and is on ventilator support," the sources also said.
Mukherjee, 84, said in a tweet in the morning, "On a visit to the hospital for a separate procedure, I have tested positive for COVID19 today."
"I request the people who came in contact with me in the last week, to please self isolate and get tested for COVID-19," Mukherjee, who was the president from 2012 to 2017, said.
Defence Minister Rajnath Singh visited the R&R Hospital and enquired about the former president's health. Singh was at the hospital for around 20 minutes.