Frenkie De Jong has pulled the inner gastrocnemius muscle in his right leg and is hence unavailable until he recovers from the injury.
Meanwhile, Gavi has fractured his right jaw and is also side-lined.
Both players started the game against Red Bull Salzburg: Gavi was replaced by Riqui Puig after 72 minutes, and Rey Manaj came on for De Jong seven minutes from the end.
The Masia youngster, who turns 17 on Thursday, has been involved in all four friendlies to date, while De Jong has appeared in all but the first against Gimnàstic Tarragona.