Jose Mourinho's men are second in the Premier League and can close the gap, at least briefly, to rivals and leaders Manchester City to five points with a win.
But Young, who came through the youth system at Watford and started his senior career at the club, is wary of Marco Silva's side.
"We know we are away, but we still want to get the three points," he said.
"The place has changed in the years since I left. They are doing well in the league, so we know it is going to be another tough game."
Watford have won back-to-back league games and sit eighth, just four points behind fourth-placed Arsenal.
Young said he enjoyed returning to his former club, but he wants a win for United.
"Of course I love going back there. I was there from when I was 10 to 21," the England international said.
"It is where I plied my trade as a kid and I learned the game in my early years so it is always nice to go back there.
"But it will be even better if we go back there and get three points."