Rusin went on the DL on July 24. He also missed time earlier this season with a strained intercostal muscle.
The 31-year-old is 0-2 with a 6.81 ERA in 35 appearances this season. Rusin made a career-high 60 appearances in 2017 and posted a 2.65 ERA.
To make room on the roster, the Rockies optioned right-hander Yency Almonte to Triple-A Albuquerque. Almonte had a 1.00 ERA in seven games spanning two stints with Colorado since he made his major league debut on June 21.