"He didn't feel as good as he hoped to. We've reconfigured the lineup and he's not in it," Hurdle said. "We'll revisit what our next move will be after the game. We're coming to a crossroads here."
Walker has dealt with lower back tightness since last Saturday. He had returned to the lineup on Tuesday, but had to leave mid-game with renewed tightness.
His pinch-hitting appearance Saturday -- he was struck out by Joaquin Benoit leading off the ninth inning of the Bucs' 2-1 loss -- would add four days to a DL stint, which otherwise could have been backdated to Aug. 6.
Hurdle waved off that aspect of the situation.
"None of us has a crystal ball," Hurdle said. "It is what it is. To second guess or get disappointed because we did something we felt comfortable doing … No, not at all. We'll move on. It's kinda the way we're built."
With Andrew McCutchen also in recovery mode from an avulsion rib fracture, the Pirates on Monday will kick off a series against Detroit in which they will confront a quartet of pitchers with 44 wins among them. That will be the start of a month-long schedule against fellow contenders.
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. Stephen Pianovich is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.