I don't mean specifically that he goes to United, but I do believe he will leave this summer.
It's his last chance, I think Benfica will let him go for something as low as 20m and I bet he will do more than Memphis did this season in just half the time if he ends up with you.
I think what made EPL team doubt him is that he is a bit slow and could be a flop for 25m+. IMO, he would be best suited for the likes of Juve/Atletico.
Don't get me wrong, I will be more than happy if he stays