Johnston sustained an apparent lower-body injury during Tuesday's joint practice with the 49ers, Kris Rhim of ESPN.com reports.
After attempting to make a contested catch, Johnston exhibited a limp, and team trainers immediately started working on the 2023 first-round pick. He hasn't exactly met expectations through three years in the NFL, including his 51-735-8 line on 84 targets in 14 regular-season games in 2025. If Johnston requires any time on the sideline, Tre' Harris, rookie fourth-rounder Brenen Thompson and KeAndre Lambert-Smith would take on elevated standing in the Chargers offense alongside No. 1 WR Ladd McConkey.