I hate to mock the dead, but for me Marc North - as a right back - really was the worst. At least Neilson's second touch was always a tackle, North never got close enough to put a tackle in.
The problem with citing a 'worst player' is that no-one can maintain being as bad as, say, Lamey for very long. I'd have said Kisnorbo was in that category until Rob Kelly took charge, and David Oldfield's final year wasn't far off either, despite him having been a good player early on in the Little era. Even Brian Carey put on a show in the 94 play-off final.