Gallen will not start Friday's Cactus League game against the Reds, Alex Weiner of Arizona Sports reports.
Gallen had been scheduled to make his spring debut March 1, but the Diamondbacks will opt to have the right-hander throw a simulated game on the back fields instead of making the trip west to Goodyear. There's no word yet on who will slot into Gallen's place for a spot start Friday.