Hartlieb was designated for assignment by the Mets on Thursday, Deesha Thosar of the New York Daily News reports.
Hartlieb made two appearances at Triple-A Syracuse after he was sent down Aug. 22, and he allowed an unearned run on two hits and two walks while striking out two in 2.1 innings. He'll be removed from the 40-man roster after the Mets claimed Brad Hand off waivers Thursday, but it wouldn't be surprising to see the 27-year-old remain with the organization if he goes unclaimed on waivers.