Here's my take on it.
Pulis has his favourites, but even by his standards, the treatment of Gnabry is something else. To publicly come out and say he's not good enough and is unfit is quite a negative statement. Even Pocognoli, Gamboa and various other players that he doesn't use have never been blasted in the press by Pulis, usually he deflects and says something cliched like they have a "good attitude" or whatnot.
Read into it what you will but I believe Pulis and don't think he'd openly lie about a players fitness, which hints that Gnabry is taking the pi$$ a bit.
What annoys me is the crying Arsenal fans, we had the same with Wisdom last year. Sorry but if they're not good enough/lazy then that is the players fault.