Johnson missed the goalless draw with Barnet last weekend with a knee injury and is still out, while captain Andy Holt remains a doubt with his own knee problem.
Striker Leon McKenzie could return to the starting line-up after being rested against the Bees and Liam Davis is available to return at left-back after recovering from a knee injury.
Former Coventry midfielder Kevin Thornton is now fit after a hamstring problem and could feature for the first time since January 8 as the Cobblers look to extend their unbeaten run to four games.
Former Darlington striker Tadhg Purcell is still sidelined with the serious knee injury which ended his season in August while midfielder Ryan Gilligan has joined Torquay on a month-long loan deal.
Source: PA
Source: PA