Fellow centre-half Darren Dennehy is another doubt for Saturday's game with Leeds, so boss Mark Stimson is looking to the youth team for a replacement.
"We're desperate, we're down to our bare bones. But we're not going to sulk over it," Stimson told BBC Radio Kent.
"We're going to look forward to the challenge and whoever gets the shirt will give it their best."
Richards' injury is a big blow for the Gills, who have already been without influential defender Simon King all season because of injury.
We've even got Dennis Oli, who has been known to play at centre-half
Mark Stimson on solving his defensive problems
"It's a broken toe which will keep him out until the end of the season," Stimson confirmed.
"He's also got ligament damage that he's had a scan on - and that might need surgery.
"That could be more serious than the four to six weeks that he's going to be out with his toe.
"Garry's got no chance this season so we're down to looking at the Connor Essams and the young Callam Davis in the reserve team game at Aldershot to see if they're available to go on the bench.
"We'll call Jacob Erskine back if his days are up at his loan spell at Croydon because I know the last couple of games he's played centre-half there.
"We've also got Tom Wynter, (midfielder) Mark Bentley and even (striker) Dennis Oli, who has been known to play at centre-half."
BBC Radio Kent will have full match commentary of Gillingham v Leeds on Saturday Sport from 1400 BST.
Source: BBC Sport
Source: BBC Sport