Morse has gone 2-for-16 on the road trip, so Endy Chavez took his place in right field in Sunday's series finale against the Rangers.
Acting manager Robby Thompson said opposing pitchers have found a weakness in Morse's swing and are going to continue hammering away at that until he adjusts.
"They're pounding him in," Thompson said. "A lot of those balls he's getting jammed on are actually balls. I think they're off the plate, in. So if he lays off those or can pull them foul with authority, then maybe they'll stay away from trying to get in there. But right now, he does need to make the adjustment in there or they're just going to continue pounding him.
"He knows that and [hitting coach] Dave Hansen and he are looking at film, trying to get him going. They're doing all the work in the cage and pregame work. Hopefully it's just a matter of time before he can kind of get back to where he was earlier in the season before he got hurt."
Morse got off to a strong start this season, hitting .248 with nine home runs with 14 RBIs in his first 25 games. But a broken finger and subsequent hamstring issue took away that momentum, as he's hit .222 with three homers and 12 RBIs in 45 games since.
"Each time he steps up to the plate, you're thinking big things can happen," Thompson said. "It just hasn't happened of late .So he'll get the day off today and we'll see where he's at tomorrow."
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.