Yelich was not in the lineup for the second straight game Wednesday night against the Pittsburgh Pirates.
The reigning National League MVP told reporters that he felt something in his back during Monday's game, when he hit his major league-leading 38th and 39th home runs.
Yelich also told reporters Wednesday that his current injury is similar to the issues that have sidelined him at various points throughout the season. He said he won't be back in Milwaukee's lineup until his back improves.
Brewers manager Craig Counsell told reporters Tuesday that he was "just being careful" by keeping Yelich out of the lineup.
Also out Wednesday for the Brewers is outfielder Lorenzo Cain, who suffered a knee injury in Tuesday's victory.