"Undisclosed illness" refers to a medical condition or sickness that someone is keeping private and has not shared or revealed to others. Full definition
President Muhammadu Buhari returned to Nigeria 103 days after he departed on yet another sick leave to attend to a still undisclosed illness. (punchng.com)
He played in the Longhorns» game against Iowa State on Jan. 1 before again exiting the lineup with an «undisclosed illness.» (sbnation.com)
Late Asake, an indigene of Southern Kaduna, died on Friday morning in Abuja after an undisclosed illness. (ghtvonline.com)