King was optioned to Triple-A Round Rock on Friday.
King will head to Round Rock after being called up May 11, having posted a 6.61 ERA and 1.59 WHIP with nine strikeouts over 16.1 big-league innings. With the Rangers acquiring Aroldis Chapman via trade from the Royals, King was the odd man out in the major-league bullpen and will look to earn another call-up later this season.