Walker, who had missed the previous 15 games with lower back tightness, said he was "close" to returning before Friday's opener at Wrigley Field.
The second baseman struck out with the bases loaded to end the sixth inning.
"He's biting to play and said he could pinch-hit today and he was frustrated he didn't get the result he wanted," manager Clint Hurdle said. "I think we're all optimistic that he could very well be in the lineup tomorrow and be ready to go."
Walker, who has been doing core and leg strengthening to make make sure his back is warm and loose, said Thursday's off-day was beneficial. He took batting practice Friday, which paved the way for his pinch-hit appearance.
"When I started to take batting practice from both sides and hit against [right-hander Jeff] Karstens [Tuesday in a simulated game], the day-after events were the big days for me and I didn't feel great after doing both of those," Walker said. "You just go on how you feel. I'll take batting practice today and see where to go from there."