"I have received information that the liver and kidney transplant surgery has been performed on uncle," Mr Dhinakaran told reporters before leaving for the hospital where 74-year-old Mr Natarajan is admitted.
Ms Sasikala had sought a 15-day parole from officials of the jail in Karnataka where she is serving her sentence to meet Natarajan, but her request was rejected on technical grounds.
Mr Dhinakaran said he was informed by their advocate that her plea for parole had been "rejected due to insufficient details." "If she seeks parole properly again, I am sure she will get it," he added.
On whether Ms Sasikala would stay at Poes Garden residence of late Chief Minister J Jayalalithaa if released on parole, Mr Dhinakaran said, "Let her come first."
Ms Sasikala continued to stay at the Poes Garden house even after Ms Jayalalithaa's died last December. She then went 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 a Rs 66.6 crore disproportionate assets case.