Born in Arbúcies, Girona, Catalonia, to Senegalese parents, Keita came up through the FC Barcelona's youth academy. In 2010, Keita travelled with the Barcelona youth team to Qatar for a tournament, where he played a practical joke by placing an ice-cube in a teammate's bed.
As a punishment, Barcelona sent the 15-year-old Keita on loan to satellite club UE Cornellà, despite Keita's reputation as a future prospect for the first team. The loan meant Cornellà held the rights to a fraction of Keita's playing rights. After a season in which he scored 47 goals for Cornellà's youth side, Keita turned down the chance to return to Barcelona, attracting the interest of Real Madrid and Manchester United.