The England Under-21 defender stepped up his recovery from ankle ligament damage by completing 90 minutes for the Foxes' reserves in midweek.
Fellow defender Patrick Kisnorbo featured alongside Mattock in the 2-1 win against West Brom and could also come into contention.
The Australian has been sidelined since suffering knee ligament damage in April but now has three second-string outings under his belt.
Barry Hayles is back at the Walkers Stadium following the end of his month-long loan spell at League One rivals Cheltenham and the veteran striker will be hoping his three goals in seven games for the Robins will be enough to earn him a place in Nigel Pearson's squad.
Midfielder Stephen Clemence and striker Paul Dickov remain out with respective ankle and back problems.
Oldham goalkeeper Mark Crossley should be fit for the clash.
The veteran was subbed at the interval against Hereford last Sunday after suffering a back spasm but has responded well to treatment during the week.
He will be replaced by stand-in shot-stopper Greg Fleming should he not be fit for kick-off.
Sean Gregan returns to the fold after completing a one-match ban while Neal Eardley makes his comeback from international duty.
Both men look set to return to the starting XI which would leave last week's back four of Kelvin Lomax, Daniel Jones, Richie Byrne and Reuben Hazell sweating on their places.
This is despite the fact they kept a clean sheet in a 4-0 win over the struggling Bulls last weekend.
Sporting Life.