The Gills have lost their last four matches - including Tuesday night's Carling Cup tie against Premier League Blackburn - and have slipped to 20th in the early League One table. But they are set to travel without Richards, who complained of a tight hamstring before the Rovers game and is still struggling.
That will mean midfielder Mark Bentley will again partner Josh Gowling at the heart of defence, with Gowling having made his loan move from Carlisle a permanent one on Wednesday.
Danny Jackman could be in line to start in midfield after he arrived back at the club from Northampton in time to be among the substitutes against Rovers, while fellow midfielder Jack Payne could reclaim his starting spot.
Stimson reverted to a 4-4-2 formation on Tuesday night from the usual 4-3-3, and may opt to keep that shape with Mark McCammon impressing alongside Simeon Jackson in attack.
Simon Royce is expected to keep his place in goal, but midfielder Stuart Lewis and defender Simon King are still a couple of months away from a return with ruptured ankle ligaments.