"The Nestlé Board of Directors was informed yesterday that Peter Brabeck-Letmathe, Chairman of the Board, has been diagnosed with an illness which is curable but requires periodic medical treatment over the next six months," the group said in a statement.
"This does not affect Mr. Brabeck-Letmathe's ability to carry out his role as Chairman of the Nestlé Board of Directors and he will continue to fully exercise his duties during the treatment period," it added.
Nestlé did not elaborate.
, the Nestlé chief had led the group's three-hour annual general meeting.
Zurich-based newspaper Blick noted that the leader had a bloodshot eye.
Brabeck-Letmathe, 69, has repeatedly said that he wants to remain at the helm of Nestlé until he is 72, the age limit set down by the group.
He has played a key role in turning Nestlé — headquartered in the Lake Geneva town of Vevey — into the global behemoth of the food and beverage sector.
Brabeck-Letmathe joined the company in 1968 as a salesman in his native Austria before working in Latin America and then moving to its Swiss base in 1987.
He became executive vice president of the group five years later, becoming known for leading Nestlé's branding strategy, which has been highly rated by the global marketing sector.
Brabeck-Letmathe became chief executive officer in 1997.
Having been elected vice chairman of the board in 2001, he then moved up to the chairmanship in 2005.
Business observers at the time questioned the wisdom of one individual holding the top posts of both chairman of the board and chief executive, and Brabeck-Letmathe relinquished the later post in 2008.