TUNIS, Jan 3 (Reuters) - Tunisia have called up uncapped Khaled Souissi and Mehdi Ben Dhifallah to their African Nations Cup training squad after the withdrawal from the tournament of two key players. Souissi, a defender with Club African, replaces French-born defender David Jemmali from Bordeaux who has a torn calf muscle. Ben Dhifallah, from African Champions League winners Etoile Sahel, comes in for Turkish-based striker Ali Zitouni, who officials said was suffering from a groin injury. Coach Roger Lemerre named a 27-man squad last month for his preparations ahead of the Nations Cup, which starts in Ghana on Jan 20 Tunisia play a warm-up friendly against Zambia at home at Rades on Sunday. Tunisia, who won the Nations Cup in 2004, are in Group D with Angola, Senegal and South Africa.