Norris, batting .400 over his last 12 games, sat on the bench Monday with right-hander Aaron Harang pitching for Seattle, allowing left-handed-hitting backstop Stephen Vogt to make his 16th start since being recalled July 25.
"We're pretty strict with it right now, but I think more than anything it's about the back issues he's been having," said manager Bob Melvin. "It started to bother him at the end of the game yesterday again, and with a left-hander going tomorrow [Joe Saunders ], it definitely makes sense to give him a day off today.
"Until we get him back and healthy, we'll try to limit him to left-handers."
Norris has 12 hits in his last 30 at-bats, just as many as he totaled in his previous 52 at-bats. Since July 1, he's hitting .346 with a .443 on-base percentage, after compiling a dismal .162 clip in the two months prior.
But so long as a firm platoon remains in place, Norris will likely only garner one start over the A's next two series against Seattle and Baltimore, with the Orioles expected to pitch three right-handers.
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.