Italy-based Samassa pulled out of the team's preparations in Bamako because of injury.
Dembele, who was born in Paris, has scored seven goals in Ligue 2 this season, prompting his first call-up by Mali.
The 24-year-old might yet not make the squad, however, as Mali coach Patrick Carteron has to cut five players before Wednesday's deadline for submitting his final 23 for the tournament in South Africa.
Mali open their tournament in Port Elizabeth on January 20 against Niger in Group B, where they also meet the Democratic Republic of Congo and Ghana.
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