Forwards Jamie Paterson, Ishmael Miller and Matt Derbyshire all came off the bench during the 1-1 league draw at Watford at the weekend and will be in contention to start the second-round tie.
Dorus De Vries' only start of the season came in the previous round against Hartlepool and he could replace Reds number one Karl Darlow in goal on Wednesday night.
Strikers Simon Cox (ankle) and Darius Henderson (thigh) could feature following their recent injury absence.
Millwall will be without Steve Morison when they head to The City Ground.
On-loan Leeds striker Morison had hernia surgery on Saturday and has been ruled out for a month.
Fellow forward Jermaine Easter is a doubt with a hamstring niggle and winger James Henry will be assessed after missing Saturday's 2-2 draw at Sheffield Wednesday through illness.
Club captain Paul Robinson could get another start as he builds up his fitness following a long-term groin injury while goalkeeper David Forde and midfielder Liam Trotter are close to returning from knee operations, but manager Steve Lomas may opt to hold them back a little longer.