The Athletics outrighted Hartlieb to Triple-A Las Vegas on Thursday.
The move clears a spot on the 40-man roster. Hartlieb got into 18 games for the Athletics this season, logging a 4.82 ERA and 22:14 K:BB over 28 frames. The 32-year-old has been outrighted before, so Hartlieb could choose to decline the assignment and become a free agent.