The Mariners said Morales was "day to day" at this point, with Alex Liddi taking his place at first base in the sixth inning. The 29-year-old switch-hitting Morales was 0-for-2 in his first two at-bats and seemed to run slowly to first base on a fourth-inning groundout to shortstop before being removed an inning later.
Morales is batting .298 with eight home runs and a team-leading 35 RBIs in 61 games. He played mostly designated hitter early in the season, but took over as the everyday first baseman when Justin Smoak strained his oblique muscle two weeks ago.
Smoak is on the disabled list and isn't eligible to return until June 14 at the earliest.
Morales was obtained in a trade with the Angels for left-hander Jason Vargas over the offseason and will be a free agent at the end of the year.