"Looking at that, I would imagine that our first would be Randy Johnson," Hall said. "Hopefully there's a lot more, but I expect No. 51 will be first."
Curt Schilling's No. 38 is unlikely to be retired because if the right-hander is elected to the Hall, it will almost certainly be as a Red Sox.
The D-backs hope that by having a strict policy they can avoid any controversies over whose number to retire.
"Because then what would the criteria be?" Hall said. "It's so subjective if it's not as concrete as making it to the Hall of Fame as a Diamondback."
While Gonzalez's No. 20 might not be retired, it's possible that no one will wear it in the near future in honor of one of the franchise's most popular players.
"There are a lot of players whose jersey won't be worn out of respect," Hall said. "We leave it up to the players. They have a choice to wear 20 or 9 or others. They typically will say, 'I'd rather have another one.' And then we'll find another number for them. They could request it, but I would be surprised if they did. Most players would stay away from them."
No one has worn No. 20 since Gonzalez left after the 2006 season, but Scott Hairston, Jeff Cirillo and Rick Schu have each worn Matt Williams' No. 9. Schilling's number was taken by Brandon Lyon, the man for whom he was traded in 2005.
As a way of honoring players who fall short of the Hall of Fame criteria, the D-backs are planning on having a Hall of Fame of their own using the space in behind the batter's eye in center field that currently houses the Peter Piper Playhouse.
The space, which was originally built back in 1998 with just such a use in mind, is ideal because it is accessible from outside the stadium and could be the place from which stadium tours begin and end. It may even contain a movie theater to show historic baseball footage.
"Hopefully very soon we'll have our new museum, which would be a perfect place to display either busts or images of players with their stats and contributions," Hall said. "But we will have more or less a D-backs Hall of Fame for great players of the past. We have lots of plans, and it could be as soon as this upcoming offseason. If not, in the next two or three years for sure."