Striker McKenzie (knee) and defender Johnson (thigh) both missed last week's FA Cup defeat at Sheffield Wednesday, but after training all week boss Ian Sampson expects the pair to be fit.
Sampson will be without Craig Hinton and Steve Guinan as they have joined Luton and Forest Green respectively on loan and Guinan's move could become permanent in January.
Striker Tadhg Purcell remains the only injury absentee and he will not feature again this season as he nurses a knee ligament injury.
The game at Sixfields looks set to beat the freezing conditions and a club statement read: "The club will continue to monitor the ongoing weather conditions but are likely to leave the pitch covers in place until as late as possible on Saturday.
"The temperatures are predicted to rise during Saturday, so the club remain hopeful that the game will go ahead as planned. No pitch inspection is currently anticipated."
Source: PA
Source: PA