On-loan Liverpool midfielder Spearing sustained a broken toe during last weekend's 2-1 win at Bristol City and will miss three weeks, while former Reds striker Ngog's season is over after he suffered a dislocated shoulder during Tuesday night's 3-2 loss to top-six rivals Leicester.
Medo Kamara and youngster Josh Vela lined-up in a five-man midfield in midweek as boss Dougie Freedman named Ngog as his lone frontman.
Vela would appear most likely to make way if Marvin Sordell and Craig Davies are selected in attack, while Tom Eaves is poised for a place on the bench once more having dislodged Kevin Davies from the matchday squad.
Wanderers' midweek loss at the King Power Stadium means they lie a point outside the play-off places with three matches remaining this season.
David Wheater (calf) is closing in on a return to fitness but fellow defender Tyrone Mears (illness) is set to remain on the sidelines alongside long-term absentee Mark Davies (knee).