Midfielder Spector missed Saturday's woeful 1-0 home defeat to Ipswich through illness but has recovered and is back in the fold to face the Robins.
Clark was less than impressed with Blues' display, especially in the first half at St Andrew's, and he will monitor those nursing niggling knocks, including Leroy Lita and Nathan Redmond, before deciding on his line-up.
Changes are almost inevitable having kept faith with the same starting XI for the last three matches.
As well as Spector, the likes of Nikola Zigic, Peter Lovenkrands, Papa Bouba Diop, Chris Burke and Darren Ambrose all come into contention.
Pablo Ibanez (broken toe) is on the verge of his comeback but Tuesday could come just too soon. Full-backs Stephen Carr (knee) and Paul Caddis (shoulder) remain sidelined.
Bristol City will be without top scorer Steven Davies for the trip to Birmingham.
The former Derby striker, who has scored six goals from just four starts, suffered a grade one hamstring tear and was unable to feature in Saturday's 1-0 defeat to Huddersfield, but there is an outside chance he could return against Charlton on Sunday.
Ex-West Ham striker Sam Baldock deputised for Davies at Huddersfield and looks set to retain his place as City aim for their first win since September 18.
Manager Derek McInnes has no fresh injury worries but Jody Morris is likely to miss out again.
McInnes was able to introduce Ryan Taylor as a substitute after the former Rotherham striker recovered from a sore ankle while Neil Kilkenny made a return to action for the first time in a month.