Ridehalgh, on loan from Huddersfield until January 12, was not given permission to play in last week's 1-1 FA Cup draw with Notts County and manager Steve Evans must decide whether to recall him at left-back or stick with Courtney Cameron, who made his fifth appearance for the club in his absence.
Striker Kieran Agard has missed the last seven games due to a thigh injury, but returned to full training this week and could make the squad.
Evans has no new injury or suspension worries, but goalkeeper Scott Shearer (knee), defenders Dale Tonge (ankle) and Craig Morgan (foot), plus midfielders David Noble (hamstring), Kari Arnason and Lionel Ainsworth (both shoulder) remain sidelined, while Mitch Rose sits out the last of his three-game ban.
The Millers boss is not expected to make many, if any, further changes to his side, who are chasing a third straight league win.
Gillingham boss Martin Allen has a couple of unnamed injury concerns to contend with.
Allen is keeping his cards close to his chest regarding their identity ahead of the encounter although he did reveal youngsters Devante McKain and Nathan Nyafli, a defender and forward respectively, have been called up to the squad.
Gills welcome back first-choice goalkeeper Stuart Nelson after he missed last weekend's 2-0 FA Cup defeat at Preston due to a one-match suspension.
Defender Connor Essam also sat out of the cup tie with a dead leg and it remains to be seen whether he will be fit to feature.
Tom Flanagan is still sidelined due to his fractured metatarsal.
Leaders Gillingham go into the clash boasting a two-point advantage over second-placed Port Vale.