The Royals optioned Bummer to Triple-A Omaha on Friday, and Bummer elected to become a free agent.
The veteran left-hander had his contract selected last weekend, and he pitched in two games out of the bullpen for Kansas City. Bummer faced 11 batters but recorded just four outs, allowing six runs on six hits and one walk with no strikeouts. He'll try to find work elsewhere rather than heading to Omaha.