Dikgacoi is on African Nations Cup duty with South Africa and Garvan is sidelined with a knee problem.
Defenders Paddy McCarthy and Joel Ward are still missing with groin injuries.
Manager Ian Holloway rested goalkeeper Julian Speroni in favour of Lewis Price in the first meeting between the sides last Saturday and could do so again.
Wilfried Zaha is expected to play amid growing speculation the winger is poised for a move to the Premier League this month.
Manchester City loanee Alex Nimely is ineligible so youngsters Alex Wynter, Jason Banton, Quade Taylor and Kwesi Appiah are set to be named on the bench again.