#1 Marcus Rashford - Manchester United
Rashford holds the ability to play anywhere in the attack, but he naturally is a goal scoring #9, who is a little undermined by his boss. Rashford has scored multiple goals while playing for the England national team as a center forward, but his goalscoring record with Manchester United hasn't been something to brag about. If Lukaku is to leave, Rashford should surely take up his position without a shadow of a doubt.
Being extremely young, extremely fit and extremely versatile, the Englishmen will then have the ability to become the next big thing for Manchester United. He has been playing mostly on the left under Jose Mourinho, but that needs to be changed as he is a fantastic finisher inside the box and can develop himself as in terms of being the next top striker. In addition, the Englishmen can also change his position depending on the situation.