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Watford visit Beautiful Downtown Bramall Lane with virtually a full-strength squad. The Hornets fought fiercely in their two games with the Blades last season, but were on the wrong ends of a 2:1 and 2:0 score-line respectively.
United have Darius Henderson, Leigh Bromby and Lee Willamson on their books, who are all ex Hornets of course. With the latter definitely out for tomorrow's (Saturday's) clash, Darius Henderson is expected to lead the line for the red and white wizards, and Mackay knows all of Darius' attributes from when the front-man was at Vicarage Road.
Mackay said: "He's a smashing lad and was with us for a number of years. It will be good to see him on Saturday.
"Our guys have trained with him, they know him and they know what he brings to the game; they've trained against him a lot too, so they know what to expect."
United said goodbye to the Carling Cup on Tuesday night, with a weakened team on show, and Mackay says that Tuesday's result will have no bearing on Saturday's game.
He continued: "I don't think it makes any difference as far as Saturday's concerned. Considering the team they had out in the week and the team that are going to play on Saturday, I don't think it makes a difference.
"We've got a tough league game to go up there and play and we know exactly what we are going to get. We've got to go there and match that.
"Come Saturday, you've got two teams who are prepared properly for it.
"Players, managers and coaches don't live and die on speculation, they live and die on what happens on the pitch on Saturday and that's what we work towards.
"All our homework should have been done by then so after that point it's about the players going on the pitch and actually performing."