United haven't won the competition since 2004, a nine-year drought Smalling is keen to end.
"I was quite shocked at how long it has been since United won the FA Cup. This club has always been successful. Luckily we have another good draw, at home to Reading, and we need to make it count.
"I don't think any game is a foregone conclusion. You have seen in the league a lot of teams down at the bottom have beaten a lot of teams at the top. It will be a difficult one but we are confident because we are playing at home.
"But this competition is difficult to win. It's about what happens on the day. Luton have reached the fifth round. Anything can happen. Form goes out of the window. It's all about what happens in those 90 minutes.
"I've seen quite a lot of Reading's games. They play good football and recently have picked up a few points. It is not going to be an easy game. We have not had too many of them at Old Trafford. We have to try and make sure we break them down."
Chris was speaking to ManUtd.com, BBC Radio and PA Sport.