Rusin was placed on the 10-day disabled list Monday with a right intercostal strain.
Rusin apparently picked up the injury during his relief appearance against the Cubs on Sunday, when he struck out four and walked one batter across 1.2 scoreless innings of work. It's unclear how long the issue will keep him sidelined at this point, but he'll be eligible to return as early as May 3 should he prove ready. Harrison Musgrave was recalled from Triple-A Albuquerque in a corresponding move and will likely take Rusin's place in the Rockies' bullpen as a long reliever for the time being.