The Diamondbacks activated Gallen (elbow) from the 60-day injured list Wednesday.
Gallen will rejoin the Diamondbacks' rotation with a start Wednesday in Kansas City after missing the past two months with right elbow inflammation. The right-hander built up to four innings and 60 pitches during a simulated game Friday, so he should be capable of 70 pitches Wednesday. Michael Soroka (shoulder) will follow Gallen in the series finale.