Oakland outrighted Kay to Triple-A Las Vegas on Monday.
The Athletics scooped Kay off waivers from the Mets on Oct. 24, but his stay on the 40-man roster didn't last long. The 28-year-old lefty has some level of pedigree to his name as a 2016 first-round pick, but he's moved into a relief role at this stage of his career and owns a pedestrian 5.59 ERA over 85.1 career innings in the majors.