Gallen (elbow) completed a 33-pitch bullpen session in Arizona on Tuesday, Alex Weiner of ArizonaSports.com reports.
Gallen was able to complete the throwing session without any issues, successfully taking the next step in his recovery from right elbow inflammation. The right-hander isn't eligible to be activated from the 60-day injured list until Sept. 7, so Gallen could throw another bullpen session or two before moving on to facing live hitters and eventually heading out on a rehab assignment.