Ter Stegen, 33, has not featured in a competitive match this season after returning from back surgery that kept him sidelined for much of 2025.
He was back on the bench for Saturday's La Liga win over Osasuna, but Flick confirmed that first-choice keeper Joan Garcia will be rested for the cup game, leaving the starting spot open between Ter Stegen and fellow contender Wojciech Szczesny.
Flick was clear about Ter Stegen's situation in his pre-match press conference. "It's his decision," Flick said, stressing that the German must decide whether he wants to stay and fight for minutes or consider other options.
"We have spoken about his situation and I respect Marc a lot because he's a great goalkeeper and a good person for the team. But in the end it is his decision, not mine."
Garcia's status as Barcelona's undisputed number one in La Liga and the Champions League this season remains unchanged, even with Ter Stegen fit again. Flick reiterated that he values all three senior keepers in his squad and praised Szczesny's contributions last season as Barcelona lifted three trophies.
The Copa tie gives Ter Stegen a rare chance to stake his claim for regular football. With Germany's manager Julian Nagelsmann reportedly making clear that his national team place depends on consistent club action, a January move has been rumoured should he not play regularly.
Team news ahead of the Guadalajara clash also indicates several changes elsewhere, with fringe players and younger talents expected to be involved as Flick manages a congested schedule. Barcelona's squad is aiming to defend their cup title while maintaining their push at the top of La Liga.
For now, all eyes are on Tuesday's cup selection, and on whether Ter Stegen will finally make his first appearance of the 2025-26 campaign or be left pondering his next career move.
Marc Casado has reshaped his role at Barcelona as the midfielder battled to protect his place and earn minutes under head coach Hansi Flick, embracing versatility as competition across the squad intensified.
Kylian Mbappe scored twice as Real Madrid survived a major scare to beat third-tier Talavera 3-2 in the Copa del Rey round of 32 on Wednesday night.
Barcelona began their Copa del Rey title defence with a hard-fought victory over third-tier Guadalajara, eventually asserting their quality to progress.
Federico Valverde and Thibaut Courtois have underlined the importance of Real Madrid's hard-fought 2-1 win away to Alaves, a result that eased pressure on the squad and kept their La Liga challenge alive after a difficult spell.
