Johnston caught both of his targets for 15 yards in Friday's 23-12 preseason win over San Francisco.
Johnston played into the second quarter and technically was the Chargers' leading receiver on a night that saw them rest all their other key players and throw for only 53 yards on 20 pass attempts. The rookie first-round pick closes out his preseason with eight caches for 62 yards and a TD on 11 targets, and he'll either be the Chargers' third or fourth wide receiver when they host the Dolphins in Week 1.