Defender Mills and forward Long played the full 90 minutes of Saturday's 2-1 home defeat to Scunthorpe, with midfielder McAnuff playing just over an hour of the match and McDermott wants to keep them all fresh for the league match at Portsmouth at the weekend.
However, Jem Karacan might be involved despite picking up a knock in the second half of the loss to the Iron.
Young attackers Jordan Obita and Lawson D'Ath have been handed squad numbers ahead of the trip to take on the Gulls and both will be included in the Royals squad.
Adam Federici, Alex McCarthy, Mikkel Andersen, Jake Taylor, Gylfi Sigurdsson, Hal Robson-Kanu and Simon Church are all unavailable as they are away on international duty.
