The Giants placed Miller on the 15-day injured list Monday due to a lower-back strain.
Miller may have tweaked his back during his last appearance against the Phillies on Thursday, when he tossed a scoreless inning in relief. The 28-year-old southpaw dealt with a back issue in spring training, so he may need a longer stint on the IL than the 15-day minimum. Right-hander Trevor McDonald was recalled from Triple-A Sacramento in a corresponding move and will start Monday's game versus the Padres.