Gallen will no longer start Tuesday's game against the Astros, Zach Buchanan of The Athletic reports.
Gallen was scheduled to make his season debut in Tuesday's series opener against Houston, but Madison Bumgarner is now listed as the projected starter for Tuesday, with Merrill Kelly scheduled for Wednesday. It's not yet clear whether Gallen is dealing with an injury or whether the Diamondbacks simply chose to adjust their rotation early in the year. The right-hander managed shoulder inflammation during the offseason that delayed his spring progression, but he was expected to avoid a trip to the injured list to begin the season.