Hartlieb was designated for assignment by the Athletics on Sunday, Jason Burke of Roundtable.io reports.
Hartlieb had his contract selected from Triple-A Las Vegas on July 18, surrendering four runs on six hits and six walks while striking out three batters over 4.2 innings in four appearances with the big-league club following his promotion. The team acquired right-handed reliever Scott Blewett from the Cardinals on Sunday, and he'll replace Hartlieb on the 40-man roster. If Hartlieb goes unclaimed on waivers, he'll likely report to Triple-A Las Vegas.