The Rays placed Kittredge (back) on the 15-day injured list Sunday.
The transaction is retroactive Thursday, three days after Kittredge made his most recent appearance out of the Tampa Bay bullpen. The Rays were hopeful that Kittredge would need only a few days of rest to overcome his bout with lower-back tightness, but he didn't progress quite as quickly as anticipated. While Kittredge -- Tampa Bay's team leader with five saves -- is sidelined, the Rays could turn to Brooks Raley as their main option at closer.