Hernandez, who ruptured an Achilles tendon at the end of August, started in an Under-23s game this week and has not been ruled out of being included.
Forward Jarrod Bowen is also expected to return to contention after missing the last two games due to a hamstring injury.
Midfielder Seb Larsson is hoping to be included in boss Nigel Adkins’ plans after a two-game ban, but Harry Wilson (shoulder), Markus Henriksen (ankle), Ondrej Mazuch (hamstring), Stephen Kingsley (groin), Moses Odubajo and James Weir (both knee) are all unavailable.
Sheffield United boss Chris wilder will make late decisions on striker James Wilson, plus midfielders Ricky Holmes and David Brooks.
Wilson missed the midweek win against QPR due to an ankle injury sustained in last week’s FA Cup defeat at Leicester, while Holmes and Brooks will both have back problems assessed.
Midfielder John Fleck and goalkeeper Simon Moore will return to contention after completing two and three-match bans respectively.
Defender Richard Stearman and striker Leon Clarke both played the full 90 minutes on Tuesday night after illness, while Ched Evans is pushing for his first start since recovering from an ankle injury.
Watford boss Javi Gracia does not think Abdoulaye Doucoure's form will be affected by his omission from France's latest squad.