Balde was heavily linked with a summer move away from the defending LaLiga champions amid concerns over his starting place after returning from injury.
Flick's decision to bring in Joao Cancelo on a permanent deal, alongside the reliability of Gerard Martin to cover at left-back, means Balde's role has been reduced.
The Spain international has only played 12 minutes in LaLiga so far this season, and Flick remains unmoved over the onus being on the player to prove himself, if he sees a future at the club.
"In my view, Balde should always show he's ready to play and send a clear message.
"I should be that 'I'm ready and, if you need me, I'm prepared', that's what I want."
Balde has been included in Flick's matchday as Barca return to matchday action away at Real Betis tonight.