Current options - Tom Cleverley, Anderson, Michael Carrick
Possible signings - Kevin Strootman, Thiago Alcantara
Forget Ronaldo, Lewandowski and Cavani - centre midfield is a massive need for United. Anderson is not fit/good/reliable (delete as appropriate) enough for a Champions League contender, and arguably neither is Tom Cleverley.
Both can play important roles in title-winning teams, but they won't stand toe-to-toe with the likes of Schweinsteiger, Xavi, Alonso - and win. They are not Champions League difference-makers.
Thiago is the one they want, because he has the potential to be exactly that. And he makes them immediately better.