The hosts are currently enjoying an eight-game unbeaten run - their longest since David Moyes took the reins in June - but have dropped points against the likes of Southampton and West Brom recently.
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"We are going into the game with a lot of confidence," Smalling told the club's official website. "We drew with Real Sociedad in the week but we had a lot of chances to win the game.
"I think we have gained a lot of confidence from our run of late. We are playing at Old Trafford and really looking forward to it.
"I don’t think there are any must-win games at this stage but it is still obviously a massive game. We are at home and we have to be the favourites to win. We have to take the game to them and show that we are the team that wants to win and close the gap."
Smalling, though, has noted the fine form of table-toppers Arsenal, but is confident himself and the rest of the United squad will be well prepared come kick-off on Sunday.
He continued: "We will look at the videos and see what they are doing well. As a defence, we will then work on things to minimise their impact but we won’t think about it too much.
"As a whole team, they are playing very well. We will find out their negatives and weaknesses, then try to punish them."