Germany Under-21 international Gnabry has played just 12 mintues of top-flight football for West Brom after joining for the 2015-16 season.
And Pulis told the Birmingham Mail: "Serge has come here to play games, but he just hasn't been for me, at the moment, at that level to play the games.
"He's come from academy football and not played much league football - does academy football really prepare players for league football? And we’re talking about Premier League football here.
"You pick your best team, you don't leave people out because you don’t like them, because of this, that and the other."