The Dodgers arrived for the game without Ethier, then announced he experienced mid-back stiffness while taking batting practice at Camelback Ranch-Glendale two hours earlier.
Ethier also came off the field the first day of full-squad workouts with a similar injury he reportedly suffered while lifting boxes before Spring Training started.
"The fact that it happened twice makes you think," manager Don Mattingly said after the game with the Mariners. "I talked to 'Dre and he said he didn't get a good stretch, but it makes you think a bit when it happens twice in [a few days]. He said something about a slide into second."
Ethier is coming off arthroscopic knee surgery in September and has had no limitations. When he's played, he's looked 100 percent. He's batting .625 (5-for-8) with two doubles, a triple, a home run and four RBIs in four games.
Mattingly said Ethier received treatment and would be re-evaluated Sunday, when he has a scheduled day off from game action.