The wide man was shown a straight red card for an altercation with Arsenal's Jack Wilshere during Tuesday's Carling Cup defeat at the Emirates Stadium and will now miss the next three matches.
Chile international defender Gonzalo Jara enjoyed an impressive debut against the Gunners at left-back and will come into contention for his first league start against the Eagles.
That comes with left-sided duo Joe Mattock and Marek Cech (both ankle) still struggling, although the former could make it in time to face Palace, while midfielder Chris Brunt remains a major doubt due to his knee injury.
Brunt's possible absence and Thomas' suspension means Robert Koren and Filipe Teixeira could keep their starting places in midfield as Youssouf Mulumbu, and a number of others rested for the cup clash, come back in.
James Morrison (heel), Neil Clement and Ishmael Miller (both knee) are not yet ready for first-team action.
Meanwhile, Crystal Palace will check on Freddie Sears and Claude Davis ahead of the trip.
On-loan West Ham striker Sears (ankle) and centre-half Davis (hamstring) both missed last weekend's 1-0 win over Derby and remain doubtful.
Young forward Victor Moses was kept on the bench on Saturday having struggled with a knee injury all week and he should come back into contention, although Sean Scannell impressed alongside Alan Lee on his first start of the season.
Austrian defender Johnny Ertl was a surprise starter in midfield against the Rams and could keep his place after a solid performance.
Strikers Stern John (elbow) and Calvin Andrew (knee) are still on the sidelines while defender Matt Lawrence has not been considered since he was transfer-listed.