Reid attempted to tackle Panthers fullback Mike Tolbert when he struck the runner's shoulder with his head and immediately went limp. Reid remained face-down on the field for some time before he was able to sit up and finally stand, then walking off the field with the assistance of trainers.
The injury is similar to one Reid sustained earlier this season when he attempted to tackle Seattle Seahawks wide receiver Sidney Rice. That hit wasn't as violent, but had the same result as Reid appeared to be knocked out on both plays.
Sunday's game between the Panthers and 49ers is a defensive affair and the score is currently 9-7 in favor of San Francisco. The team will turn to five-year safety C.J. Spillman. Spillman, who has been used primarily on special teams, has 15 tackles this season.