CAIRO, Jan 17 (Reuters) - Tunisia have called up St Etienne defender Alaeddine Yahia to replace the injured Karim Saidi in their squad for the African Nations Cup finals in Egypt, the Tunisian Football Federation said on Tuesday.Saidi, who played a key role when Tunisia won the Nations Cup on home soil two years ago, was injured in training with his Dutch club Feyenoord last week and has not recovered in time. French-born Yahia, 24, was also a member of Tunisia's squad at the last Nations Cup but played in just one match. He is the sixth player from French club St Etienne to be called up by a competing side at this year's tournament. Tunisia open the defence of their title with a match in Group C against Zambia in Alexandria on Sunday. The Nations Cup starts on Friday and runs until Feb. 10.