The winger pulled up with a hamstring strain just before half-time during the 1-0 defeat at Doncaster on Saturday and faces up to three weeks on the sidelines.
Gavin Williams replaced Sproule last time out and is the most likely player to deputise in his absence.
Evander Sno is set to return from suspension but it remains to be seen whether captain Louis Carey will be back after a groin problem.
Johnson otherwise has a full-strength squad to choose from as the Robins look to improve on their recent run of form that has seen them win just one of their last seven league games.
