They crashed 3-0 at Valiant Park on Tuesday night, as injuries and suspensions threaten to disrail their push for promotion.
"We were 2-0 down before we really got going, and that's not good enough," blasted Sheridan.
"The players have got to show more of a ruthless streak. Port Vale got stuck into us and some of my players didn't fancy it.
"I wasn't happy with myself for getting sent to the stands and we are picking up too many bookings, which could cost us."