The Rockies placed Stephenson on the 10-day injured list Monday with upper-back tightness.
Lefty Ben Bowden was summoned from Triple-A Albuquerque to fill Stephenson's spot in the Colorado bullpen. Over 27 relief appearances in his first season with the Rockies, Stephenson has posted a 4.56 ERA and 1.56 WHIP across 23.2 innings.