"I don't know how I hurt it," said Moss. "I was coming onto the field [in the top of the third], and it just balled up on me, and I couldn't really get the cramp out for the entire inning. It was hurting pretty badly.
"I figured if I can't get the cramp out, I should probably get it taken care of. You never know. Hopefully it's just a bad cramp or something, nothing more than that."
The A's first baseman hit his first career grand slam in his first at-bat before flying out in his second.
Kyle Blanks replaced him in the bottom of the third inning, finishing 1-for-2 with a walk.
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.