Rashford is only 24 years old, he is a talented player, I think there will be plenty of time for him to show his best form and continue to develop with Manchester United.
He still underperforms even in the National (England) team, If he still does not give the best between the time, I'm really sure his name is not inside in World Cup 2022. that age is very crucial for a player to go the best or trash, as we know Balotelli, he has talent but he not trying to give them what he has. Same as Rashford, he is the future but hasn't found a coach yet that suits him, this is an opportunity to fill up as Ronaldo's partner, if he can't he will be one of them.