Watford are likely to to make changes to the squad that faced Gillingham in mid-week after they fielded a weaker team.
However Defender Matt Jackson is unlikely to feature after suffering a concussion during the 3-0 victory over the League One side.
Possible Hornets Line-Up: Mart Poom, Jordan Stewart, Lloyd Doyley, Danny Shittu, Jay DeMerit, Lee Williamson, Jobi McAnuff, Gavin Mahon, Tamas Priskin, Tommy Smith, Marlon King.
Sheffield United are likely to make key changes with new signings Gary Naysmith (knee) and Lee Hendrie (cartlidge) both out injured whilst Rob Hulse (broken leg) is awaiting his return.
Possible Blades Line-Up: Paddy Kenny, Derek Geary, Chris Lucketti, Matthew Kilgallon, Keith Gillespie, Michael Tonge, Nick Montgomery, Chris Armstrong, James Beattie, Jonathan Stead.