The Red Devils, who are 12 points clear in the Premier League title race, are one game away from reaching the quarter-finals of the Champions League following their 1-1 draw with Real Madrid in the first leg of the round-of-16 clash last Wednesday.
The North-West outfit can reach the final eight of the FA Cup too if they clinch a win over Reading in the fifth-round tie this evening.
"The manager has stressed that he expects to go to the end in all three competitions," Sky Sports News quotes Smalling as saying.
"The FA Cup is notoriously unpredictable. Luton reached the fifth round this year, which shows that anything can happen so there is no point looking too far ahead.
"But our home form has been good and another victory can give us the impetus to kick on and get to another final."
If United knock Reading out of the Cup, they will face either Middlesbrough or Chelsea in the next round.