Manager Lloyd McClendon revealed that Ackley has been dealing with a stiff back the last few days, which may explain his absence from Wednesday's lineup, Ryan Divish of the Seattle Times reports. The Mariners have a scheduled off day Thursday, so by leaving Ackley out of the lineup Wednesday, the hope his he'll be fine with two days out of the lineup. Expect him to return to outfield duties when the Mariners kick off their weekend series with the Red Sox on Friday.