The Red Devils opted to allow the 26-year-old to leave Old Trafford towards the end of the summer transfer window as Lukaku linked up with Antonio Conte in Serie A.
Manchester United made three main signings this summer after having completed deals for Harry Maguire, Aaron Wan-Bissaka and Daniel James.
However, Ole Gunnar Solskjaer was unable to add another striker to his squad before Thursday’s deadline, despite Lukaku leaving the club late on in the window.
And former Arsenal star Smith feels that the Red Devils would have been wise to try and bring in a new forward in the summer transfer window.
Speaking in an interview with Sky Sports, Smith rated Manchester United’s summer business as a “B” and said: “The addition of Maguire is important to add some authority to that defence if he can produce what he has done for Leicester and Wan-Bissaka is a very good young player.
“But with Romelu Lukaku going, the question is: should they have brought in another striker to replace him? So I do not think they have done all that they wanted.”
Manchester United will kick off their Premier League campaign with a testing clash against Chelsea FC at Old Trafford on Sunday afternoon.
The Red Devils will have their sights focused on breaking back into the top four this term after they finished sixth and without a trophy last season.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news