His wife, Mira Bhattacharya, has also reportedly tested positive for the virus. She has been admitted to a private hospital in Kolkata.
Notably, Buddhadeb has been suffering from Chronic Obstructive Pulmonary Disease (COPD) and was discharged from the hospital few months ago.
According to doctors, his oxygen level is fluctuating but doctors are keeping a close watch on him.
Meanwhile, former President Pranab Mukherjee's son Abhijit Mukherjee wished a speedy recovery to the octogenarian.
"Wishing a speedy recovery to respected former Chief Minister Buddhadeb Bhattacharya," he tweeted in Bengali.
Trinamool Congress MLA from Barrackpore, Raj Chakrabarty also wished good health to the former CM and tweeted, "Praying for the good health and speedy recovery of you and your family. Get well soon sir."
Bhattacharya was West Bengal Chief Minister for 11 years from 2000 to 2011.
India added 267,334 new cases of COVID-19 in the last 24 hours, taking the tally to 25,496,330.
Meanwhile, even as COVID cases decline in the country, high fatality rate remains a worry. India reported a national record of 4,529 new deaths. The country has been reporting over 4,000 deaths per day due to COVID-19 for over a week now.