John, currently on a two-month loan deal from Southampton, featured as a second-half substitute in the goalless draws with Barnsley and Sheffield United but Johnson could turn to the Trinidad & Tobago international to solve his side's goal drought.
The Robins have not conceded a goal in four consecutive games but have also found the net just three times in their last five Championship outings.
John is likely to lead the line alongside Nicky Maynard but defenders Jamie McAllister and Louis Carey remain sidelined with toe injuries.
Scotland international McAllister has been boosted by the news he has not suffered a broken metatarsal and will return to full training next week.
Reading boss Steve Coppell has no fresh injury or suspension concerns.
Marek Matejovsky (ankle) is not 100% fit but is still aiming for a place on the bench, while Michael Duberry (calf) has recovered from his injury but is not yet match fit.
Duberry is likely to need a reserve game under his belt before returning to first-team action but is a possibility for a place among the substitutes.
Graeme Murty (calf) is progressing well but is still a few weeks away from a return, fellow defender Alex Pearce has been allowed to join Southampton on loan.
The Royals' home form has been superb this season but they have struggled on their travels, picking up just one win from their seven games so far.