Saunders went 0-for-2 in his first two at-bats, including a bases-loaded strikeout in the third against Erik Bedard, then was replaced by Dustin Ackley when Seattle took the field in the top of the fifth.
"I felt my shoulder, I don't even know how to really explain it, but I felt it on a swing and it was uncomfortable," said Saunders. "I came in here [to the training room] and did some stuff. We don't expect it to be anything serious; I'm pretty confident in that and we'll reevaluate tomorrow."
The 27-year-old has been one of the Mariners' hottest hitters in their recent surge, batting .356 (21-for-59) with three home runs, 18 RBIs and 11 runs scored over his past 17 games.
Saunders is hitting .280 on the season with four home runs and 25 RBIs.
Left fielder Cole Gillespie moved to right field after Saunders' departure, with Ackley taking over in left.
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.