Saunders was at the plate in the eighth inning of Thursday night's game against the Twins when he checked his swing and experienced pain in his side. He left the game in the middle of his at-bat.
The 27-year-old is hitting .276 on the season with six home runs and 28 RBI in 65 games.
Seattle also recalled first baseman Justin Smoak from Triple-A Tacoma. Smoak owns an average of .208 with seven home runs and 29 RBI in 63 games with the Mariners this season.