Vargas allowed two runs over five innings Tuesday night and spent a long time in the trainer's room after the game. The team said then his back was being treated. On Friday, his injury was listed as a left flexor strain.
Recently acquired catcher Drew Butera joined the club following his trade from the Angels and right-hander Yohan Pino was recalled from Triple-A Omaha. Catcher Francisco Pena had been optioned to Omaha following Thursday's win over Cleveland.