Miguel Montero will be the starting catcher, with Henry Blanco and Tuffy Gosewisch battling for the backup role.
With outfielder Cody Ross looking like he might be healthy for Opening Day, and Gerardo Parra, Mark Trumbo and A.J. Pollock locks for the roster, it leaves one spot open, with Tony Campana, Alfredo Marte, Matt Tuiasosopo and Shelley Duncan among the candidates.
Given that Ross is coming back from a dislocated and fractured right hip, the D-backs are leaning toward carrying a fifth outfielder rather than another backup infielder.
"Probably more an outfielder than an infielder, just because Cody, I think if he is healthy and ready to go, we're not going to want to overdo it with him right off the bat," Towers said.
Tuiasosopo's versatility could work in his favor, as he can also play third base as well as first.
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.