Matip fails to join Cameroon squad
The Schalke 04 midfielder did not travel to Nairobi where Cameroon will play a warm-up against Kenya on Saturday before travelling on to Angola.
Team officials said the 18-year-old, who has a Cameroonian father and German mother, had not received a passport in time.
However the country's sports minister said he had sought permission to join up late with the squad due to a school exam.
His club coach Felix Magath said the call-up for Matip had come as a surprise.
"In our view it makes no sense he travels there," Magath told the club's website.
Matip scored on his Bundesliga debut against Bayern Munich in November.
His 24-year-old brother Marvin, who plays for Cologne, had also previously been called up by Cameroon but could not play for the African country as he has represented Germany at junior level.
Cameroon open their Nations Cup campaign in Lubango next Wednesday when they meet Gabon in Group D.
They also face Tunisia and Zambia in the first round.