Event-related potentials (ERPs) have been useful to detect subtle, pervasive alterations of cognition-related waveforms in athletes with multiple concussions. This study used the sustained posterior contralateral negativity (SPCN) waveform component recorded while participants performed a visual short-term memory task to investigate how working memory (WM) storage capacity was affected among athletes who differed according to their history of sports concussions. Fifty-five university-level football players were assigned to three groups: 1-2 concussion athletes; 3+ concussion athletes; non-concussed athletes. The main finding of the present study was that athletes with a history of three concussions or more exhibited significantly attenuated SPCN amplitude relative to both concussed athletes with only one or two prior concussions and athletes without concussions. The latter finding adds to previous evidence of disproportionately worse outcome in athletes presenting with a history of three or more concussions relative to those with fewer concussions. In addition, SPCN amplitude was found to correlate significantly with a visual memory capacity estimate (K), but this K value did not significantly differ across groups. This suggests that attenuated SPCN amplitude after three or more concussions did not interfere with apparent WM function. Taken together, these findings suggest that the altered neurophysiological index of WM storage might be a more sensitive measure of a latent WM function abnormality which may well worsen with aging, or perhaps additional brain insults.