Striker Johnson is nursing an ankle injury and defender Havern has been ill, making them doubts for the short trip across the Pennines.
Midfielder Matty Mainwaring remains sidelined after he broke a leg during pre-season but is ahead of schedule in his recovery.
County have moved into mid-table in League One after collecting four points from their last two outings.
And Ablett has urged his young side to believe in themselves when they head to the Galpharm Stadium.
He said: "We seem to be going in the right direction at the moment so we'll wait and see how we get on against Huddersfield."