The centre-back twisted a leg during Saturday's 4-0 FA Cup loss at Gillingham, with Niall Canavan likely to come back into the starting XI alongside Paul Reid if necessary.
Even if Mirfin is fit, manager Brian Laws is expected to make a number of changes to his side.
Steve Mildenhall is likely to make his debut in goal, having joined on loan from Millwall on Monday. Sam Slocombe will drop to the bench, with James Severn left out of the matchday squad altogether.
On-loan pair Leon Clarke and David Prutton are also expected to come back into the starting XI, having been ineligible to play at Priestfield on Saturday.
Clarke's return is particularly vital, having taken on the Iron's goalscoring burden virtually single-handedly this season with seven goals already to his name.
Walsall will be without Florent Cuvelier (hamstring), while Febian Brandy (knock) and Andy Taylor (hamstring) are unlikely to feature.
All three missed Saturday's 1-1 FA Cup first round draw at non-league Lincoln City, where a late goal from George Bowerman rescued a replay for the Saddlers.
Dean Smith's side have not won in their last eight games,