Belt's condition was uncertain before the start of play Sunday, but the first baseman hadn't quite recovered from getting hit in the face when he arrived at Marlins Park. He was tested for a concussion shortly after.
Only team doctors checked him out after Saturday's victory over the Marlins. Belt, who was fielding at first during batting practice when the accident occurred, left that game in the third inning with dizziness, a headache and nausea.
Manager Bruce Bochy said it was possible that South Florida humidity triggered Belt's symptoms. He'd been fine and ended up pulling a double into the right-field corner in his first at-bat. Belt, who returned July 4 after missing 50 games with a broken thumb, had gone 4-for-11 over his last four games.
"You have no choice in a concussion situation," Bochy said. "It's a bad break for Brandon, who is coming off the DL. My guess is that running to second and third activated it. He was doing pretty well [before that]."
Maria Torres is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.