The Athletics designated Thomas for assignment Saturday.
Thomas joined the Athletics on Thursday after being claimed off waivers from Atlanta, but the left-hander didn't make any appearances before the Athletics elected to move him off the 40-man roster. The 28-year-old has gotten off to a historically poor start to his big-league career; over four appearances with Milwaukee and Atlanta between this season and last, Thomas has allowed 27 earned runs on 27 hits and eight walks while striking out nine batters in 11.2 innings.