O'Toole sat out last weekend's 2-0 home defeat to Sheffield United with a one-match suspension after picking up five bookings this season but is available again to face the Eagles.
Striker Grzegorz Rasiak started against the Blades in place of Tamas Priskin but failed to hit the target so Rodgers may change things around.
Loanees Gavin Hoyte, Jack Cork and Liam Bridcutt are all available after being given permission to play in the competition by respective parent clubs Arsenal and Chelsea.
Midfielder Lee Williamson is fit again after a recent ankle knock but goalkeeper Mart Poom (shoulder) and Gareth Williams (knee) remain long-term absentees. Winger Lionel Ainsworth has joined League One side Huddersfield.
Neil Warnock is considering tinkering with his defence at Vicarage Road.
The Eagles boss was critical of centre-halves Matt Lawrence and Jose Fonte after last weekend's 4-1 defeat at home to Ipswich and may move Clint Hill into the middle and bring Danny Butterfield in at left-back.
Warnock will be without midfielder Ben Watson, who is on the verge of leaving Selhurst Park with Middlesbrough leading the race for his signature.
Watson has been sidelined lately with a calf injury so three of Shaun Derry, Nick Carle, John Oster and Neil Danns will again form the midfield.
Defender Paddy McCarthy is recovering from a shoulder operation and was this week told he could be back in action by March.
The two sides met at Vicarage Road in the third round last season with a Danny Shittu brace enough for the Hornets to progress.