"It started up earlier and then just got worse," said Parker. "Starting to progressively get worse. … I'm hoping to be back pretty soon."
Gorkys Hernandez assumed Parker's spot in the lineup and in left field in the Cardinals' half of the fifth inning.
"I don't want to say oblique yet, it's just tightness on the left side," Giants manager Bruce Bochy said. "We'll leave it at that. It's probably going to be a couple days, at least. But I'll know tomorrow. Could be more."
Entering Friday, Parker boasted a .344 average at home and had 10 hits in 25 at-bats with runners in scoring position. Parker missed 96 games earlier this season after fracturing his clavicle.
Jonathan Hawthorne is a reporter for MLB.com based in the Bay Area. This story was not subject to the approval of Major League Baseball or its clubs.