McCombe was forced to withdraw from the Robins squad against Watford on Boxing Day with pelvic and stomach problems and a late decision will be made on his fitness.
Dele Adebola staked his claim for a recall against his former club by scoring as a second-half substitute at Vicarage Road.
Adebola, a Palace player between August 2002 and June 2003, had been sidelined with a dead leg but marked his return to the squad with an injury-time goal in the 4-2 victory over Watford to challenge Stern John and Lee Trundle for the right to partner Nicky Maynard in attack.
City's win against the Hornets was their first in nine league matches and boss Gary Johnson is targeting another three points against Palace to end 2008 on a high note.
"If we can get a victory then things will look a lot rosier than they did before Christmas," Johnson said. "Hopefully we'll be able to get the right result and finish the year on a high. Maybe that will stop people talking about our recent form."
Crystal Palace are without Clint Hill and will check on Paddy McCarthy ahead of the trip to Bristol.
Left-back Hill is suspended after he was booked for the fifth time this season, while centre-half McCarthy faces a late fitness test.
The Irishman has put off a shoulder operation in order to keep playing over the festive programme, but had to be substituted during the second half against Norwich on Friday.
"We may give him one more go but we'll have to wait and see," said Eagles boss Neil Warnock.
Matt Lawrence and Danny Butterfield are the likely candidates to step into the back four.
Midfielder Ben Watson (hamstring) is unlikely to be fit so Palace should otherwise be unchanged from the side which beat the Canaries 3-1.