Note. I've already had to revise this piece several times since I wrote it on Saturday morning. If the D-backs pull any further surprise moves out of the hat between scheduling and publication, it's not my fault, dammit!
The candidates
In alphabetical order, these are the players currently outside the 25-man roster, but eligible for call-up on September 1st are as follows, along with their current level:
It's a list heavily skewed towards the mound, with 12 of the 15 being pitchers; the only exceptions being Brito, Drury and Romak. It's also heavily dominated by Reno Aces, who have two-thirds of the players eligible on their roster.