Barcelona announced on Thursday that Neymar will be out for four weeks after a bruise led to swelling on the fourth metatarsal of his left foot.
The club also announced that Jordi Alba has a right hamstring injury and could be out three to four weeks.
The injuries would appear to rule both players out of the league games against Athletic Bilbao, Villarreal and Getafe, and raises doubts over their ability to feature in the final two games, which come at Elche on May 11 and then at home to Atletico Madrid on May 18.
Brazil's Neymar and Spain's Alba should both be back fit in time for the World Cup starting on June 12.
Centre-back Marc Bartra has also been battling a right hamstring injury and did not train on Thursday. His participation in Sunday's match vs. Athletic is uncertain.
Neymar was visibly hobbling after Wednesday's 2-1 loss to Real Madrid in the Copa del Rey final. Neymar smashed the post in Barca's last goal attempt, but the ball landing safely in the hands of Iker Casillas before any Barca players could capitalise.
Due to the injuries, Barcelona coach Tata Martino added four players from Barca B for training: Sergi Gomez, Carles Planas, Edgar Ie and Frank Bagnack.