On-loan West Ham striker Sears suffered an ankle injury against Scunthorpe last weekend and ex-Rams defender Davis is struggling with a hamstring problem.
The duo would have missed Tuesday night's trip to QPR but the match was called off, so they have had an extra few days to recover but remain doubtful.
Palace can welcome back centre-half Paddy McCarthy, who sat out the 4-0 home defeat by Scunthorpe through suspension.
Veteran defender Matt Lawrence is unlikely to make the squad having been placed on the transfer list in the wake of Saturday's drubbing, while strikers Stern John (elbow) and Calvin Andrew (knee) are still missing.
Meanwhile, young striker Matthew Wright has joined Ryman Premier outfit Maidstone United on loan.
Wright, who arrived at Palace in the summer as a free agent and signed a one-year deal, has agreed a one-month loan switch and goes straight into the squad for Maidstone's away fixture at Boreham Wood.
Eagles boss Neil Warnock told the club's official website: "This is a good opportunity for Matthew to get some matches under his belt at a good level."
Manager Nigel Clough has confirmed new signing James Vaughan will play some part in Derby's game at Palace.
The 21-year-old has moved to Pride Park on a three-month loan deal from Everton to help ease the Rams' striker problems with Steve Davies (ankle) still out and Chris Porter (hip) and Giles Barnes (Achilles) long-term absentees.
"Team-wise it is a boost to have another body available to us," said Clough. "With Rob Hulse, Kris Commons, Paul Dickov and James Vaughan we have some excellent options open to us.
"It is up to us now to decide who we start on Saturday, but I think James will certainly play some part in the game."
Meanwhile, the club have confirmed that Jake Buxton requires a hernia operation. The defender has been experiencing discomfort in his stomach and tests have revealed the problem.
He could be out for up to six weeks - approximately the same amount of time as midfielder Paul Green who has suffered a setback in his recovery from a foot injury.
Sporting Life