Midfielder Niven will be assessed having been forced off in the 53rd minute of last Friday`s goalless draw at Torquay with a jarred ankle.
Forward Morgan, meanwhile, missed the Plainmoor encounter altogether with a thigh strain but is hoping to return for the final day clash at a sold-out b2net Stadium.
Fit-again defender Simon Ford returned to enjoy a starting role in what was his first match in over two months against the Gulls and he has not suffered any ill-effects.
The Spireites go into the game knowing just a point will be enough to get their hands on the League Two title while second-placed Bury must win at Stevenage to have any chance at all of overtaking John Sheridan`s side at the summit.
But Gillingham, unbeaten in 11 away from home, go into the clash needing the points themselves, with the Kent club one of three sides on 68 points competing for two remaining play-off berths.
Source: PA
Source: PA