Full-back Gray completes a two-match ban for collecting 10 yellow cards this season and centre-half Charles serves a one-match suspension after he was sent off against Bournemouth in midweek.
But James Dunne returns from a ban and fellow midfielder Gavin Mahon hopes to shake off the knock which kept him out of Tuesday night's 1-0 defeat.
Boss Gary Smith has also recalled defender Bondz N'Gala and striker Dani Lopez from their loan spells at Barnet.
Lee Hills should keep his place in the side in Gray's absence while N'Gala or Andy Iro, who also had a loan stint with Barnet recently, could step in for Charles.
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