"Anything could happen when Graham Westley comes to town," Johnson told BBC Radio Northampton.
"I don't think we're on each other's Christmas card list. He's got his own style. You've got to win the battle on and off the pitch."
Northampton are set to be withouon-loan goalkeeper Steve Collis and top goalscorer Leon McKenzie for the clash, after both sustained thigh injuries in t 2-2 draw with bottom club Stockport County.Chris Dunn may be fit to return to first-team action, after stitches were required to a serious head injury against Bury.
"We'll be looking to see if we can get [Chris] back," said Johnson.
"He might have to wear one of those 'Phantom of the Opera' masks. [Youth goalkeeper] Paul Walker has done well, he's a good shot stopper. But against a Stevenage side, you probably need someone more than 6ft tall."
Source: BBC Sport
Source: BBC Sport