Barca's Ter Stegen faces three months out after back surgery
The Spanish champions signed Espanyol goalkeeper Joan Garcia this summer, who is expected to become the team's first choice, with Wojciech Szczesny as back-up.
"Today is a personally difficult day for me. Physically and athletically, I feel in very good shape, although unfortunately I am not free from pain," said Ter Stegen on social media network Instagram.
"After intensive discussions with the FC Barcelona medical team and external experts, the quickest and safest way for me to fully recover is through back surgery.
"After my last operation on my back, I returned to the pitch after 66 days-almost two months... this time, the doctors believe about three months will be necessary as a precaution, to avoid any risks."
Spanish media reported Barcelona were hoping to sell Ter Stegen, 33, who signed for the club in 2014, to help register new signings Garcia and Marcus Rashford.
Last summer a long-term injury to defender Andreas Christensen allowed Barcelona to use a La Liga loophole to register playmaker Dani Olmo on a temporary basis after he signed from RB Leipzig.
"Emotionally, it hurts a lot not being able to support the team during this time. Fortunately, the rehabilitation is manageable and the road back is clear," continued Ter Stegen.
"Don't worry -- I'll be back."