Eighty-year-old Dayalu Ammal's counsel said she is "weak and bed-ridden" and it would not be possible for her to leave her house and come to the court.
Special CBI Judge O P Saini issued a notice to CBI and sought its reply by tomorrow on the application.
The application said her medical records indicate she is suffering from Alzheimer disease and is undergoing treatment for the past one year.
It also said if the court feels, it can constitute a medical board to examine Dayalu Ammal and give its report on her condition.
In its second charge sheet filed on April 25, 2011, CBI had named Dayalu Ammal as a prosecution witness in the case in which DMK MP and M Karunanidhi's daughter Kanimozhi is facing trial along with others, including former Telecom Minister A Raja.
