Gallen (elbow) will return from the 60-day injured list and start Wednesday's game against the Royals, Jody Jackson of DBacks.tv reports.
Wednesday will mark Gallen's first appearance of the second half, as the 31-year-old has been on the shelf since July 12 due to right elbow inflammation. He pitched 1.2 scoreless innings in a rehab game at Triple-A Reno on Aug. 30 before building up to four innings and 60 pitches during a sim game Friday. Rather than waiting for Gallen to get fully stretched back out, the Diamondbacks will instead have him make what will likely be an abbreviated start Wednesday before turning the ball over to right-hander Michael Soroka (shoulder), who will also be activated from the IL to pitch in the series finale in Kansas City.