Hollowell (forearm) has struck out four while allowing one hit and two walks over two scoreless innings in his two appearances since being activated from Triple-A Albuquerque's 7-day injured list May 16.
Hollowell missed the first month and a half of the season while recovering from right forearm tightness. The 25-year-old retains a spot on the Rockies' 40-man roster and has prior experience in the big leagues, so he could emerge as a candidate for a promotion to the Colorado bullpen if he can continue to string together quality appearances with Albuquerque.