The clash is a repeat of last season's fifth round tie which was won by the Royals after a replay after a thrilling 2-2 draw at the Madejski.
Reading benefited hugely from their Cup run last season but McDermott is concerned at the number of games some of his first team have had to play recently and is considering changes.
In-form striker Shane Long has scored six goals in his last five games but is expected to be rested due to a bruised foot, with Simon Church coming into the side.
Veteran full-backs Andy Griffin and Ian Harte are also likely to be given a rest, while club captain Ivar Ingimarsson could feature for the first time all season as he recovers from a serious hamstring injury. His Icelandic compatriot Brynjar Gunnarsson is still out with a knee injury.
Goalkeeper Adam Federici could also be given the weekend off with one of Alex McCarthy and Mikkel Andersen given the chance to impress after Andersen returned from his loan at Bristol Rovers. On-loan QPR midfielder Mikele Leigertwood is available to play but remains a doubt with a hamstring problem.