Walker held an ice pack to his right side and was also being given medication for what he said began as a "cramping feeling" early in Saturday's game against the Cubs. He went 0-for-2 and made one play in the field -- turning a line drive into a double play -- before leaving in the bottom of the fifth.
"I just felt something. I didn't know what it was, but I wanted to be careful," he said. "I've talked to a couple of the other guys who've had something similar, and they said you just have to give it a couple of days to calm down and go from there. I don't expect it to be anything extended."
"He's day to day and will be re-evaluated by our doctors," manager Clint Hurdle said.
The veteran Brandon Inge started Sunday's game at second base, and made a fine defensive play for the final out of the first inning.
Tom Singer is a reporter for MLB.com and writes an MLBlog Change for a Nickel. He can also be found on Twitter @Tom_Singer. This story was not subject to the approval of Major League Baseball or its clubs.