Fulham winger Williams and Newcastle midfielder Richardson arrived on loan deals on Thursday to boost manager Martin Allen's squad.
Leading scorer Danny Kedwell again misses out with a hamstring injury which is expected to keep him sidelined for around three weeks.
Midfielder Charlie Allen will be assessed having sustained a wrist problem in Tuesday's goalless draw at York. He had shrugged off an ankle complaint to take part at Bootham Crescent.
Boss Allen is also waiting on a couple of players struggling with illness and bumps and bruises but is keeping his cards close to his chest regarding their identity.
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- Danny Kedwell