The Rangers optioned Pennington to Triple-A Round Rock on Tuesday.
Pennington has been solid out of the bullpen since joining the Rangers in August, posting a 2.76 ERA and 1.59 WHIP through 16.1 frames. However, he gave up three earned runs in just two-thirds of an inning during his most recent appearance, which will ultimately cost him his spot on the active roster. Josh Sborz (shoulder) returned from the 15-day IL in a corresponding move to take Pennington's place.