Yelich appeared to aggravate it while running out his grounder to short in the first inning. He was shown rubbing his lower back in the dugout before being tended to by training staff.
Reed Johnson entered as a defensive substitution in the top half of the second.
Following the game, Yelich said his back actually began to lock up on Gregory Polanco's leadoff single to left-center that he reached down to grab.
"Tightened up for the rest of the inning," Yelich said. "Tried to hit, tried to run to first and it was at half speed as hard as I could go."
The 22-year-old is batting .259 with six homers and 24 RBI in 63 games. Since going hitless in four straight contests earlier this month, Yelich is 10-for-24 (.417) with three doubles, a homer and five RBI during a five-game hit streak. He had moved from the leadoff spot to second in the order on Friday with the debut of Rafael Furcal.
Yelich said he stretched, ran sprints and threw before the game and "felt fine." He has never had back spasms before.
"It feels tight," Yelich said. "I'm not getting around here too fast right now. Hopefully wake up tomorrow and it feels better. We're doing everything we can. I think we're just going to have to wait and see."