Baez left Saturday's game against the Pirates with back tightness, Jesse Rogers of ESPN.com reports.
Baez went 1-for-3 at the plate prior to exiting with the injury. It doesn't sound like a particularly serious one, but the shortstop could still find himself on the bench for at least one game. The Cubs have an off day Monday, so he'll wind up with two consecutive days of rest if he sits out Sunday.