The left-back had spent much of the summer insisting he wanted to stay at Camp Nou, but sources report he has now given agent Jorge Mendes the green light to explore an exit, with João Cancelo's return leaving him short of regular football under Flick this season.
Asked directly about Balde's future at a press conference, the German coach stopped short of backing the 22-year-old's continuity.
"It's a difficult question because he has enormous quality, and it's important to know whether a player is convinced he can compete in his position," Flick said. "That's what I want to see from all my players.
"Every day I see what the players do, their level, whether they show me they're at the level to play. In the end, you have to play as a team, only then will we have success.
"I need everyone to be one hundred per cent."
Flick added that further squad changes should not be ruled out with the window entering its final stretch.
"There can be changes and we'll have to wait until the end of the transfer window," he said, leaving Balde's situation, along with those of Héctor Fort and Marc Casadó, unresolved with just over a week of trading left.
Cancelo's permanent arrival has significantly increased competition for the left-back berth, with the Portuguese able to operate on either flank and already trusted by Flick's coaching staff, leaving Balde at risk of starting the season without a settled role in the side.
Manchester United have been credited with tracking his situation, while Benfica are reported to be readying an offer worth close to €20 million, according to Sport.
Balde, a graduate of La Masia who signed a contract extension carrying a €1 billion release clause in 2023, has been an established first-team regular for Barcelona since breaking through under Xavi Hernández.