OAKLAND -- Brandon Moss exited Friday's 9-5 win against the Angels in the third inning with right calf tightness.
Manager Bob Melvin deemed Moss day to day after the game and said he was likely "doubtful" for Saturday's contest.
"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.