The 28-year-old struck out looking in his first two at-bats before being removed for pinch-hitter Logan Morrison. Morrison remained in the game at first base, while first baseman Mark Trumbo moved to right field, right fielder Seth Smith moved to left and left fielder Dustin Ackley moved to center.
"The [second] strikeout looking was more in regard to the way his back felt as opposed to his approach at the plate," Jewett said.
Jewett said Jackson first felt his back tighten up on defense but felt better after stretching. Jackson's back tightened up again when he returned to the outfield and stood around in the innings leading up to his exit.
Jackson is 2-for-10 during the Mariners' current homestand and hit his first career grand slam on Tuesday night. He has hit safely in 25 of his last 36 games and is hitting .268 (37-for-138) during that span.