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 due to 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 around 70 pitches. Michael Soroka (shoulder) was also activated from the IL and will work behind Gallen in Wednesday's series finale.