Treinen (shoulder) will report to Triple-A Oklahoma City on Friday to begin a rehab assignment, Kirsten Watson of SportsNet LA reports.
Treinen pitched against live batters over the weekend and will now embark on a minor-league rehab assignment. The veteran right-hander has been sidelined by the shoulder injury since mid-April, so he'll likely require numerous rehab outings before being reinstated from the 60-day injured list.