The 23-year-old has missed Barcelona's last two games, having last played in their 4-0 win over Mallorca on June 13.
Sources have told ESPN that there is no timeline set for his return.
The midfielder has played in 38 games for Barcelona this season after joining the club from Ajax for €75 million last year.
Should Madrid beat Real Sociedad on Sunday, they could leapfrog the Catalan club on points difference.
In the Champions League, Barcelona will face Napoli in the newly formatted tournament being held from Aug. 12-23.
Sources have told ESPN that Barca will only be able to use money from the sale of players to make other signings this summer.
Barca president Josep Maria Bartomeu has said the club would still be "capable" of landing the game's best players, but he warned deals could be structured in a very different way after the crisis.