The Swami, on dialysis for the last few months for kidney problem, suffered from pneumonia and was on ventilator support till yesterday, Dr Nalla G Palanisami, Chairman, Kovai Medical Center and Hospital (KMCH), told PTI.
Since he had developed some breathing problem, doctors attending to him had to remove part of a lung, he said.
"At present the 83-year old Swamiji is slowly recovering and his condition improving," Palanisamy said.
Tamil superstar, Rajinikant is an ardent disciple of the Swami.