The Swiss champions have paid €990,000 for the 25-year-old, who made more than 200 appearances for Sfax. Ba grew up in Dakar, Senegal before joining the Tunisian club aged just 17, and had been a first-team regular since 2000. Sfax won a league and cup double last season and reached the African Champions League final.
Basel coach Christian Gross has also snapped up Ecuador forward Felipe Salvador Caicedo Corozo in a pre-contract agreement. The 17-year-old, recruited from Rocafuerte Fútbol Club, cannot sign a full contract until his next birthday.
Caicedo shone at the South American Under-17 Championship in Venezuela earlier this year, and has already won his first cap for the senior Ecuador team.
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