Gary Johnson said: "There is quite a bit of swelling and bruising around the ankle and Brad is probably going to be out of the frame for a week or two. But we have got able replacements to cover for his absence."
Republic of Ireland under-21 captain Richard Keogh replaced Orr at the City Ground and Johnson admits playing the youngster at right-back against Rovers is an option.
"Richard did well when he came on and he is a lot closer to being a natural right-back than he was when he first started playing there.
"Although he is naturally a centre-half, he is certainly an option."