Brown is available for Sunday's game against the Los Angeles Dodgers.
Masset was placed on the disabled list with a left patellar tendon strain after pitching in Saturday's win over the Dodgers. Masset is 1-0 with a 4.94 ERA in 28 appearances this year. He missed the previous two seasons with a right shoulder injury that required thoracic outlet surgery.
The 29-year-old Brown was 1-0 with a 4.35 ERA and six saves in 31 appearances for the Sky Sox this year. He was signed as a free agent in the offseason. He has never appeared in a major league game.
To make room for Brown on the 40-man roster, the Rockies designated right-hander Raul Fernandez for assignment.