Manager Craig Counsell said after Sunday's 5-0 win over the Nationals that Happ was scratched from the lineup due to lower back tightness, Tim Stebbins of MLB.com reports.
Happ was set to start in left field and bat in the leadoff spot, but his back issue forced him to sit for Sunday's series finale, and the 30-year-old outfielder is considered day-to-day with the injury. Since Sept. 1, Happ has slashed .284/.333/.395 with two home runs and nine RBI over 87 plate appearances.