Deciding on a worst player is always a difficult one I think. To me it's not just as simple as worst player ever seen(which would be Gary McVie)it's more worst player that made a number of appearances and therefore continued to look the antithesis of a footballer over a period of time rather than just one game or a couple of sub appearances.
I saw McVie play once(badly), Kelechie Okorie likewise.
Neil Orr was pish for a while, Brian Smith played infrequently and was always crap, Jim Gardner was consistently awful.
Taking all into consideration I'd have to give a joint equal award to Mo Camara and Mikael Renfrum.
Both wage thieves of the highest order.