Striker Howard was forced out of the midweek defeat to Bournemouth with a hamstring strain, midfielder Sweeney sustained a knee injury after just five minutes in the same match and right-back Richards missed out on Tuesday night due to a knee problem.
Neil Austin will continue in place of Richards if the teenager fails to make it.
James Poole and teenager Luke James will be vying for a place in the starting line-up if Howard fails a fitness test, while defender Jack Baldwin and winger Andy Monkhouse are also pushing for recalls.
Poole and Charlie Wyke, on loan from Middlesbrough, both sustained knocks against Bournemouth, but are expected to be in contention as John Hughes' side chase their third league win of the season.
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