In a short statement, Atalanta said the forward had hurt the lateral joint in his right knee and would not travel to Spain where on Wednesday the Italians are aiming to secure direct qualification for the last 16 of the Champions League.
Atalanta later added that Lookman would be sidelined for "around three weeks", a huge loss for Atalanta as he has scored 14 goals and set up six more this season.
He also scored a hat-trick in last season's Europa League final triumph over German champions Bayer Leverkusen.
Atalanta have punched well above their weight both in Italy and abroad in recent seasons.
Gian Piero Gasperini's side are still Serie A title contenders, they are seven points adrift of leaders Napoli, and riding high in Europe's elite club competition.
The Bergamo-based outfit sit seventh in the 36-club league phase of the Champions League, but with a host of clubs within a point of them, anything but a win at already-qualified Barca will likely mean a playoff spot.
