Harrison’s men are four points off league leaders Featherstone Rovers and need a win to keep in touch with the top two.
But Harrison rates Murrell, who suffered a broken hand three weeks ago, as having only a 20 per cent chance of facing the Knights.
Harrison said: “It is all a question of how much pain Scott feels with the injury. We’ll assess him nearer the time.”
Matty Nicholson remains sidelined for York, but is edging closer to a return from shoulder surgery and could feature within the next three weeks.
James Ford (knee) is also missing as coach Gary Thornton aims to bounce back from last week’s 20-4 home defeat against Whitehaven.
Thornton said: “It was a very, very frustrating performance. We tried hard defensively, but we just couldn’t crack them open.”