The midfielder was booked for the fifth time this season in the midweek goalless draw with Nottingham Forest and must now serve a one-match ban.
On-loan defender Toni Kallio has failed to recover from illness, while striker Darius Henderson is still struggling with a hip injury.
Goalkeeper Mark Bunn is likely to retain his place between the sticks due to injuries to Ian Bennett (thumb) and fellow loanee Carl Ikeme (calf).
Blackwell told the club's official website: "Toni was sent home by the doctor on Thursday because he is still showing signs of tonsilitis, but overall we are looking at the same squad we had out against Forest."
Neil Warnock has no new injury worries to contend with for Crystal Palace's trip.
Centre-half Paddy McCarthy is the only absentee after undergoing a shoulder operation last week which will keep him on the sidelines for around three months.
Warnock reshuffled his back four at Reading in midweek, with Clint Hill reverting to centre-half on his 100th appearance for the club and youngster Nathanial Clyne recalled at full-back.
The Eagles boss could stick with that line-up after Clyne was on target in an impressive 4-2 win.
Teenage striker Victor Moses, who Warnock expects to leave in January, scored twice and will keep his place.
Young defender Lee Hills could make the bench after serving a three-match ban for a red card while on loan at Oldham.
Sporting Life