United have won the competition for the last two seasons and, with Chelsea, Manchester City and Liverpool all having bowed out in round three, are big favourites to triumph once more.
"There's definitely a sense of the cup being there for the taking when you look at the teams that have gone out," Smalling told United Review.
"When we got back on the coach at Scunthorpe we couldn’t believe City and Chelsea had gone out and we watched Liverpool lose on penalties [to Northampton Town]. We all sense there’s a good opportunity to win the trophy and that’s our aim."
The young defender fired his first United goal in the last round at Scunthorpe as the Reds came from behind to book their spot in Tuesday night's fourth round