Natarajan had been undergoing treatment at a corporate hospital for the past few days.
"I have received information that the liver and kidney transplant surgery has been performed on uncle," Dhinakaran told reporters here before leaving for the hospital where 74- year-old Natarajan is admitted.
Confirming the news, Dhinakaran said that he was informed by their advocate that her plea for parole had been "rejected due to insufficient details."
"If she seeks parole properly (with required documents) again, I am sure she will get it," he added.
When asked if Sasikala would stay at Poes Garden residence of late Chief Minister Jayalalithaa if released on parole, Dhinakaran said, "Let her come first," and asked where would the scribe who posed the question wanted Sasikala to put up.
Sasikala had continued to stay at the Poes Garden residence even after Jayalalithaa's demise last December.
She proceeded from there to Bengaluru in February to surrender before a local court after the Supreme Court upheld a lower court judgement sentencing her to four years in jail in the Rs 66.6-crore disproportionate assets case.