Robertson was left off the Phillies' roster for the National League Division Series matchup with Atlanta due to a strained right calf, Todd Zolecki of MLB.com reports.
Robertson reportedly suffering the injury when jumping in the air to celebrate Bryce Harper's homer in Game 2 of the wild-card series against the Cardinals. He received a platelet-rich plasma injection, which could help him return for the NLCS, should the Phillies advance, but the team will be without one of its top bullpen weapons against Atlanta.