Orr missed last weekend's draw with Sheffield Wednesday with the calf injury suffered against Barnsley the week before, and he could replace midfielder Cole Skuse who has been deputising for him.
City go into the clash sitting in fifth place in the table and could end the weekend in second depending on other results.
The Robins are unbeaten at home in 19 games, but have only one once on their travels this season, so manager Gary Johnson will be looking for them to improve their away form, starting against Forest.
Liam Fontaine is again set to sit out with an ankle injury while Brian Wilson (shin) is a long-term absentee.
