Kolarek was designated for assignment by the Athletics on Thursday.
Kolarek was sent down by Oakland in late May, and he'll lose his spot on the 40-man roster just over a month later. The southpaw has posted a 5.68 ERA and 1.23 WHIP in 12.2 innings over 11 appearances at the Triple-A level, and he'll likely remain in the organization if he goes unclaimed on waivers.