Sancho's rumoured 25 million euros fee isn't that huge honestly. The real problem is his salary... Why?
Because he makes 7.8 million pounds (~9.2 million euros) a year at Manchester United. Chelsea didn't even pay his full salary during their loan contract.
Is Napoli or Juventus keen on paying this much money per year to him?

I don't know whether he is keen on taking a pay cut.
Manchester united are the ones overpaying these players for nothing, and they have become a pain on the ass for United in offloading them. Sancho should accept a pay cut and leave United since he's not adding any value to the club. Maybe, when his contract expires, he will go for a higher pay which I don't think is possible. No club will pay him what United is paying him with his current performance.
Manchester United is one of the miserable clubs in world where they are having history of overpaying for players those never deserve amount which Red Devil's pays for them and then have pain in the a** currently things are on their lowest level.
Amorim is having too many challenges with few players were over paid but now have no recovery option, but they needed to be settled this and look forward which can give them better option few players are good for Serie A, but they are not able to pay which Manchester United pay in the past. Few players are had salaries which are surely not any other club can give them, but they are not looking for salary cut which is also problem, but they needed to do some decisions which give them relief.