The duo missed last week’s 4-2 win over Wigan Athletic at Bramall Lane, which sent the Blades top of the Championship.
Record signing John Egan was absent with a hamstring problem, while midfielder Duffy was nursing a hip injury.
But United manager Chris Wilder - without Chris Basham who serves a one-match ban for collecting five bookings - is optimistic the pair will be fit to travel to the City Ground.
“John will hopefully be ready for Saturday, and Mark Duffy as well,” said Wilder.
“We want to be at full strength, but we will give them as much time as possible to make that decision.”