Realmuto aggravated a back injury during Saturday's 3-1 loss to Atlanta, Charlotte Varnes of The Athletic reports.
Realmuto went hitless in two at-bats before being lifted in the sixth inning Saturday, but according to Varnes, the catcher initially suffered the injury in Friday's series opener during a play at the plate. He is expected to be re-evaluated early Sunday, at which point the Phillies will have a better feel for whether the veteran backstop will require a stint on the the injured list.