Morse, 31, will rejoin the Mariners on Tuesday as Seattle kicks off a six-day East Coast road trip through Boston and Baltimore. Morse hit .250 (6-for-24) with a double, one home run, two RBIs, two walks and six strikeouts over six games with the Rainiers.
The slugger had been on the disabled list with a strained right quadriceps since June 22. He initially suffered the injury on May 28, then appeared in 11 of Seattle's next 23 games before being placed on the disabled list. Morse has hit .251 with 11 homers and 23 RBIs in 56 games for the Mariners this season.
The Mariners have 10 days to trade, release or outright Bay to the Minors. The 34-year-old outfielder, signed as a free agent in December, has appeared in 68 games this season, batting .204 with 11 homers and 20 RBIs.
Adam Berry is a reporter for MLB.com. Follow him on Twitter at @adamdberry. This story was not subject to the approval of Major League Baseball or its clubs.