Midfielder Derry sits out with a one-match ban after he was booked for the fifth time this season against Nottingham Forest last weekend so Martin Rowlands, Gavin Mahon or Mikele Leigertwood will come in.
Full-back Orr serves the final game of his three-match ban for his red card against Reading last month.
Tottenham loanee Kyle Walker is struggling with an ankle knock so striker Jamie Mackie, who scored for Scotland in midweek, may have to fill in at right-back again.
Matt Connolly returns from a one-match ban and should line up at centre-half, allowing Clint Hill to revert to left-back.
Heidar Helguson's neck injury will be checked over but Georgios Tofas (hamstring), Akos Buzsaky, Peter Ramage and Lee Cook (all knee) are still missing.
Source: PA
Source: PA