Gallen (elbow) completed a 30-pitch bullpen session Tuesday and is tentatively scheduled for another session Friday, Zach Buchanan of The Athletic reports.
The 25-year-old was able to throw all his pitches during Tuesday's session, which is a good sign as he attempts to return from a UCL sprain. Gallen should continue building up to a starter's workload over the next few weeks before potentially rejoining Arizona's starting rotation.