Hemmings missed the goalless draw at Sky Bet League Two rivals Cambridge on Saturday with a hamstring problem, but could be back in contention.
Stags boss Steve Evans reported no fresh injury problems as they prepare to take on the Championship side, with the winners set to host Premier League leaders Manchester City in a televised fourth-round tie.
Central defender David Mirfin continues his recovery from a knee problem.
On-loan Cardiff midfielder Craig Bryson is back in full training, but will probably not be risked after Achilles trouble.
Bluebirds boss Neil Warnock plans to give Bryson and Kadeem Harris, who has not played this season following ankle surgery, match practice behind closed doors this week.
Sol Bamba is an option after missing the first game against the Stags, while Brian Murphy could retain his place as Cardiff’s cup goalkeeper.
Loan signing Yanic Wildschut is cup-tied having played for Norwich in the Canaries’ third-round tie against Chelsea.
Manager Chris Wilder has warned it may take some time before Sheffield United bring in any new faces this summer.