Johnson left Friday's practice early and went back to the locker room on a cart, Mark Kaboly of The Athletic reports.
There's no initial indication of a serious injury, with Brooke Pryor of ESPN.com noting that it's a good sign Johnson was sitting in the front seat of the trainer's cart rather than riding in the back. Dale Lolley of the Steelers' official site agrees the injury didn't look serious and reports that Johnson briefly returned to practice after first getting hurt. The 27-year-old is expected to operate as one of QB Kenny Pickett's top receiving options again, though the Steelers may want to scale Johnson's volume back a bit after he saw 147 targets last season without scoring a touchdown and falling short of 900 receiving yards.