Zambian President Michael Sata, who left for medical treatment abroad at an undisclosed destination this weekend, will miss the southern African nation’s 50th independence anniversary celebrations, his deputy said on Tuesday.

Vice-president Guy Scott told parliament that acting president Edgar Lungu would lead a wreath-laying ceremony at the Freedom Statue in the capital and at other activities that should have been presided over by Sata on Oct. 24.

Sata, 77, left Zambia for an undisclosed country on Sunday night accompanied by his wife and family members. A terse government statement gave no further details.

Concern over Sata’s health has been mounting in Africa’s second-largest copper producer since June when he disappeared from the public eye without explanation and was then reported to be getting medical treatment in Israel.

Sata missed a scheduled speech at the U.N. General Assembly in September amid reports that he had fallen ill in his New York hotel. A few days before that he had attended the opening of parliament in Lusaka, joking: “I am not dead.”

Sata has not been seen in public since he returned to Zambia from New York around Sept. 28.