Baker has been sidelined since sustaining an ankle injury at Arsenal on the opening day of the Barclays Premier League season, while fellow defender Luna picked up a knock in Saturday's defeat to Liverpool. Charles N'Zogbia (Achilles) remains a long-term absentee.
Manager Paul Lambert has vowed to send out a strong side as Villa look to make up for the disappointment of last season's semi-final exit to lower league Bradford.
Rotherham will be without suspended striker Daniel Nardiello for their Capital One Cup clash with Aston Villa.
Nardiello stepped off the substitutes' bench to earn the Millers a point against Shrewsbury at the weekend, but was shown a second yellow card for protesting after the final whistle and sits out a one-game ban.
Winger David Worrall missed out at the weekend due to a groin strain and remains doubtful, but manager Steve Evans has no other new injury or suspension worries.
First-half goals from Ben Pringle and Lee Frecklington earned Rotherham a 2-1 win over local rivals Sheffield Wednesday in the first round.