Marc-Andre ter Stegen will be out two to three weeks with an injured back.
The 22-year-old keeper is viewed as Barcelona's long-term replacement for Victor Valdes.
A Barça statement read: "The first team goalkeeper Marc-Andre ter Stegen, following persistent pain in his lower back caused by a blow received in training last Monday, August 11, has been subjected to new medical tests this morning which have revealed the existence of a small fracture in the transverse apophysis of vertebra L3.
"The club's medical services reported that the player will be out for between two and three weeks. The player will carry out recovery work during this period."