Garver was scratched from Seattle's lineup ahead of Tuesday's game against Kansas City due to upper-back spasms, Daniel Kramer of MLB.com reports.
The 33-year-old backstop missed a few games in March due to back spasms, though manager Scott Servais said Garver's current injury is unrelated to his previous issue. No timeline was given for his return, but it's possible the M's hold him out for a game or two in order to allow him to properly recover.