Gnabry was handed his first senior start at Emirates Stadium on Saturday as Arsenal came from behind to draw 2-2 with Napoli - and the German teenager provided a spark from the right flank, going close on two occasions in the first half.
"What I see is the potential," the manager told Arsenal Player.
"I don't have many opportunities to make these players realise what is needed at the top level. I can only use the pre-season games in that and that is where they can see 'oh, what a shock that is, the level I have to get to' and to get used to that pace.
"That's why I try to use these kind of games. You want of course to prepare well, not lose the games, and of course give experience to young players. Sometimes that is very difficult."