Centre-half Barnett completed a two-game ban by missing the 1-0 home win over leaders QPR while left-back Lappin served a one-match suspension.
The duo could come in for Zak Whitbread and Adam Drury, who made their first starts after long injury absences against Rangers, although their fine displays will have given manager Paul Lambert a welcome selection dilemma.
Wes Hoolahan will continue in midfield if David Fox is not fit.
Defender Elliott Ward (calf) and midfielders Henri Lansbury (hamstring) and Andrew Surman (knee) are out.
Lambert must also decide whether to stick with three forwards - Aaron Wilbraham, Chris Martin and Grant Holt - at The Riverside.
Source: PA
Source: PA