Centre-half Cooper had to be substituted just before half-time in Monday's 2-2 draw at the Proact Stadium.
Richards came off with 15 minutes remaining after the striker's two goals against his former club had put the Spireites in the lead.
Assistant manager Tommy Wright said: "With Liam Cooper, we don't think it's as bad as we first feared.
"It's more of a kick than a twist. He's got a bit of a gash on his ankle so we're quite hopeful with that.
"Marc Richards is a bit more of a twist, though, so it will take longer to assess."