O'Connor received a straight red card in the weekend defeat at MK Dons and starts a three-game ban, while fellow midfielder Frecklington sits out one match after reaching five yellow cards.
Michael Tidser could be recalled in their absence with Kari Arnason pushed up into midfield alongside him, with either Mark Bradley or Pablo Mills stepping into the heart of defence, but much depends on the tactics of boss Steve Evans.
Tom Eaves is also pushing for a start and could replace Alex Revell up top whilst there could be a return for Daniel Nardiello.
David Worrall (groin) remains sidelined as does big Claude Davis who is still suffering with hamstring trouble.
Ian Goodison joins the growing list of Tranmere absentees for the clash. The veteran defender will be out of action for three games following his red card in the 4-0 drubbing by Leyton Orient at the weekend.
Joe Thompson (illness), Sam Ramsbottom (ankle), Evan Horwood (groin) and Jean-Louis Akpa Akpro (abscess) are still ruled out, leaving Moore with a skeletal squad to choose from for his return to the Millers.
Jason Koumas may be in line for a return to action after he was named among the substitutes on Saturday after recovering from a groin strain.
Both sides are currently struggling for form and will be looking for a vital three points to move up the League One table.
Source: PA
Source: PA